CHEM 321 - ANALYTICAL CHEMISTRY Le Chatelier's principle and equilibrium shifts Question Bank Set 6

CHEM 321 - ANALYTICAL

CHEMISTRY - Le Chatelier’s principle

and equilibrium shifts

Question Bank - Set 6

Liberty University

Question 1

Question

Consider the following equilibrium reaction at a certain temperature:

2 SO2(g) + O2(g)⇌2 SO3(g)

If the concentration of SO2is increased by a factor of 3, predict the direction

in which the equilibrium will shift. Justify your answer.

Solution

Step 1: Write the equilibrium expression for the reaction: The equilibrium

expression for the given reaction is:

K=[SO3]2

[SO2]2[O2]

Step 2: Analyze the effect of increasing SO2concentration: When the con-

centration of SO2is increased by a factor of 3, the new concentration of SO2

will be 3[SO2].

Step 3: Use Le Chatelier’s Principle to predict the equilibrium shift: Accord-

ing to Le Chatelier’s Principle, if the concentration of a reactant is increased, the

equilibrium will shift in the direction that consumes that reactant. Therefore,

the equilibrium will shift to the right to consume the excess SO2.

Therefore, as the concentration of SO2is increased by a factor of 3, the

equilibrium will shift to the right to reach a new equilibrium position.

This shift will result in an increase in the concentrations of SO3and O2at

the new equilibrium state.

Question 2

Question

For the reaction N2O4(g)⇌2NO2(g)at equilibrium, ∆H= +57.2kJ.

If the equilibrium constant Kc= 0.82 at 25◦C, how will the equilibrium shift

when the temperature is increased? Justify your answer.

Solution

Step 1: Given data. The equation for the reaction is: N2O4(g)⇌2NO2(g)

∆H= +57.2kJ (endothermic reaction)

Kc= 0.82 at 25◦C

Step 2: Le Chatelier’s Principle When the temperature is increased in an

endothermic reaction, the equilibrium will shift towards the products side to

absorb the added heat.

Step 3: Justification Since the reaction is endothermic, increasing the tem-

perature will favor the endothermic reaction to absorb the excess heat. The

equilibrium will shift towards the products side (2NO2) to counteract the in-

crease in temperature.

Therefore, the equilibrium will shift to the right (towards the products) when

the temperature is increased.

Question 3

Question

For the reaction:

H2O(g)⇌2H2O(l)

What effect would each of the following changes have on the position of the

equilibrium (shift to the left, shift to the right, or no change)? Justify your

answers.

(a) Increasing the pressure by decreasing the volume of the container.

(b) Adding a catalyst to the reaction vessel.

(d) Increasing the temperature of the reaction vessel.

Solution

(a) Increasing the pressure by decreasing the volume of the container:

•Step 1: According to Le Chatelier’s principle, increasing the pressure on

a system at equilibrium will cause the equilibrium to shift in the direction

that reduces the total number of gas moles.

•Step 2: In this case, the reaction involves the conversion of gaseous water

to liquid water, so decreasing the volume (increasing pressure) will shift the

equilibrium to the right to reduce the pressure by decreasing the amount

of gaseous water.

•Step 3: Therefore, increasing the pressure by decreasing the volume of

the container will shift the equilibrium to the right.

(b) Adding a catalyst to the reaction vessel:

•Step 1: A catalyst does not affect the position of the equilibrium. It only

speeds up the rate at which equilibrium is reached but does not change

the position of the equilibrium.

•Step 2: Therefore, adding a catalyst to the reaction vessel will have no

effect on the position of the equilibrium.

•Step 1: According to Le Chatelier’s principle, if a reactant or product

is removed from a system at equilibrium, the equilibrium will shift in the

direction to replace the substance that was removed.

•Step 2: In this case, liquid water is being removed, which is a product of

the reaction. Therefore, the equilibrium will shift to the left in order to

produce more liquid water.

•Step 3: Removing some of the liquid water from the reaction vessel will

shift the equilibrium to the left.

(d) Increasing the temperature of the reaction vessel:

•Step 1: When the temperature of a system at equilibrium is changed,

the equilibrium will shift in the direction that absorbs or releases heat in

order to counteract the change in temperature.

•Step 2: In this case, the reaction is endothermic (heat is a reactant).

Increasing the temperature will favor the endothermic reaction to absorb

the added heat, so the equilibrium will shift to the right.

•Step 3: Therefore, increasing the temperature of the reaction vessel will

shift the equilibrium to the right.

Question 4

Question

For the reaction:

2 NO2(g)⇌2 NO(g) +O2(g)

Which gas will cause an increase in the concentration of NO2at equilibrium?

Justify your answer using Le Chatelier’s principle.

Solution

Step 1: According to Le Chatelier’s principle, if a stress is applied to a system at

equilibrium, the system will respond by shifting the equilibrium to counteract

the stress.

Step 2: In this reaction, the concentration of NO2can be increased by either

increasing the concentration of NO or O2.

Step 3: Increasing the concentration of O2will shift the equilibrium to the

left, favoring the formation of NO2.

Step 4: Thus, increasing the concentration of O2will cause an increase in

the concentration of NO2at equilibrium.

Therefore, the gas that will cause an increase in the concentration of NO2

at equilibrium is O2.

Question 5

Question

Consider the following reaction at equilibrium:

2 SO2(g) + O2(g)⇌2 SO3(g)

If the pressure of the system is increased by decreasing the volume, predict

the direction in which the equilibrium will shift. Justify your answer using Le

Chatelier’s principle.

Solution

Step 1: Identify the effect of decreasing volume on the system.

Decreasing the volume of the system will increase the overall pressure within

the system.

Step 2: Apply Le Chatelier’s principle. - In this reaction, the increase in

pressure from a decreased volume will shift the equilibrium to counteract the

increase in pressure. - According to Le Chatelier’s principle, the system will

respond by favoring the side of the reaction with fewer gas moles to decrease

the pressure.

Step 3: Analyze the reaction. - On the reactant side, there are 3 moles of

gas (2 moles of SO2 and 1 mole of O2). - On the product side, there are 2 moles

of gas (2 moles of SO3).

Step 4: Determine the direction of the equilibrium shift. - Since the reactant

side has more gas moles, the equilibrium will shift to the left to decrease the

pressure by consuming some of the gas-phase reactants.

Therefore, if the pressure of the system is increased by decreasing the volume,

the equilibrium will shift to the left to relieve the pressure increase.

This shift to the left will result in an increase in the concentrations of SO2

and O2 and a decrease in the concentration of SO3 until a new equilibrium is

established.

Question 6

Question

In an aqueous solution, the reaction 2 HgCl2(aq)⇌2 Hg(s) + Cl2(g)is estab-

lished at equilibrium. If the volume of the container is suddenly decreased, pre-

dict how the equilibrium will shift according to Le Chatelier’s principle. Justify

your answer.

Solution

Step 1: Identify the factors that can affect the equilibrium: The factors to

consider include concentration, temperature, and volume changes.

Step 2: Analyze the effect of decreasing the volume on the system: When

the volume of the container is decreased, the system will try to counteract this

change by shifting the equilibrium to reduce the pressure.

Step 3: Determine the side of the reaction that has fewer gas molecules: On

the reactant side, there are 2 moles of gas (all in the form of Cl2gas), while on

the product side, there is only 1 mole of gas (the Cl2gas).

Step 4: Predict the direction of the equilibrium shift: Since decreasing the

volume increases the pressure, the system will shift the equilibrium to the side

with fewer gas molecules to alleviate some of the increased pressure. Therefore,

the equilibrium will shift to the right (towards the products) to decrease the

total number of gas molecules.

Step 5: Justify the answer: The reaction will proceed in the direction that

will decrease the total number of gas molecules to counteract the increased

pressure due to the decrease in volume. Thus, the equilibrium will shift towards

the products (Hg and Cl2) to establish a new equilibrium position with a lower

total gas pressure.

Question 7

Question

Consider the following equilibrium reaction:

2SO2(g) + O2(g)⇌2SO3(g)

At a certain temperature, the equilibrium constant, Kc, for this reaction is

0.56. If a reaction vessel initially contains 0.50 M of SO2, 0.25 M of O2, and 0.20

M of SO3, what will be the change in each of the concentrations at equilibrium?

Solution

Step 1: Let’s define the initial concentrations and changes in concentration as

follows: - Let xbe the change in concentration for both SO2and O2(since they

both decrease) and 2xbe the change in concentration for SO3(since it increases

by a factor of 2). - The initial concentrations are:

[SO2]initial = 0.50 M

[O2]initial = 0.25 M

[SO3]initial = 0.20 M

Step 2: Using the information above, we can set up an ICE (initial, change,

equilibrium) table for the reaction:

Compound Equation [Compound]initial Change [Compound]equilibrium

SO22SO2(g) + O2(g)⇌2SO3(g) 0.50 −x0.50 −x

O22SO2(g) + O2(g)⇌2SO3(g) 0.25 −x0.25 −x

SO32SO2(g) + O2(g)⇌2SO3(g) 0.20 +2x0.20 + 2x

Step 3: Now, we can write the expression for the equilibrium constant, Kc,

in terms of the concentrations at equilibrium:

Kc=[SO3]2

[SO2]2[O2]= 0.56

Substitute the equilibrium concentrations into the equation above and solve

for x.

Step 4: Once you have found the value of x, you can calculate the equilibrium

concentrations for each compound. Subsitute the value of xinto the expressions

derived in the ICE table.

Therefore, the change in each of the concentrations at equilibrium can be

determined.

Question 8

Question

For the reaction

N2O4(g)⇌2NO2(g)

at a certain temperature, the equilibrium constant Kcis 0.42. If the concen-

tration of N2O4at equilibrium is 0.25 M, what is the concentration of NO2at

equilibrium?

Solution

Step 1: Write the equilibrium expression for the reaction:

Kc=[NO2]2

[N2O4]

Step 2: Given that Kc= 0.42 and [N2O4] = 0.25 M, we can rearrange the

equilibrium expression to solve for [NO2]:

0.42 = [NO2]2

0.25

Step 3: Solve for [NO2]:

[NO2]2= 0.42 ×0.25

[NO2]2= 0.105

Step 4: Take the square root of both sides to find [NO2]:

[NO2] = √0.105

[NO2]≈0.324 M

Therefore, the concentration of NO2at equilibrium is approximately 0.324

Question 9

Question

A gaseous equilibrium is established according to the reaction:

N2(g)+3H2(g)⇌2NH3(g)

If the pressure of N2is decreased at constant temperature, predict in which

direction the equilibrium will shift. Justify your answer.

Solution

Step 1: Determine the effect of decreasing the pressure of N2. According to Le

Chatelier’s principle, decreasing the pressure of a system will cause the equilib-

rium to shift in the direction that produces more moles of gas to compensate

for the pressure change.

Step 2: Examine the stoichiometry of the reaction. On the reactant side,

there are 1 mole of N2and 3 moles of H2, totaling 4 moles of gas. On the

product side, there are 2 moles of NH3. Therefore, the forward reaction (to the

right) produces more moles of gas.

Step 3: Conclusion. Since decreasing the pressure of N2will shift the equi-

librium towards the direction that produces more moles of gas, the equilibrium

will shift to the right (towards the products) to increase the total gas moles and

alleviate the pressure decrease.

Question 10

Question

Consider the following reaction at equilibrium:

2 HgCl2(aq)⇌2 Hg(s) + 2 Cl−(aq)

If additional solid Hg is added to the system at constant temperature and

pressure, predict how the equilibrium will shift. Justify your answer using Le

Chatelier’s principle.

Solution

Step 1: The addition of solid Hg will cause the reaction to shift towards the

reactants in order to counteract the increase in the concentration of Hg.

Step 2: According to Le Chatelier’s principle, an increase in the concen-

tration of a reactant will cause the equilibrium to shift in the direction that

consumes that reactant.

Step 3: In this case, the reaction consumes Hg to form HgCl2, so the equi-

librium will shift to the left to produce more HgCl2.

Step 4: As a result, additional solid Hg will cause the equilibrium to shift to

the left, favoring the formation of more HgCl2attheexpenseofHg.

Step 5: Thus, the equilibrium will shift to the left when additional solid

Hg is added to the system at constant temperature and pressure in order to

maintain equilibrium.

Question 11

Question

For the reaction CO(g) + H2O(g)⇌CO2(g) + H2(g), which will result in an

increase in the equilibrium constant if the pressure is increased?

Solution

Step 1: First, let’s determine the change in moles of gas when the reaction shifts

towards the products in response to an increase in pressure. Since one mole of

CO and one mole of H2O will result in two moles of gas, and one mole of CO2

and one mole of H2 will only result in two moles of gas as well, the total change

is 0 moles of gas. Therefore, the reaction will not shift towards the products in

response to an increase in pressure.

Step 2: According to Le Chatelier’s Principle, if the pressure is increased and

the reaction does not shift towards the products, then the system must try to

counteract the change in pressure by shifting in the opposite direction. In this

case, the system will shift towards the reactants when the pressure is increased.

Step 3: Since the reaction shifts towards the reactants in response to an

increase in pressure, the concentration of CO and H2O will increase, while the

concentration of CO2 and H2 will decrease. This will result in an increase in

the numerator and a decrease in the denominator of the equilibrium constant

expression, ultimately leading to an increase in the equilibrium constant.

Therefore, the equilibrium constant will increase if the pressure is increased

for the reaction CO(g) + H2O(g)⇌CO2(g) + H2(g).

Question 12

Question

A gaseous equilibrium system is described by the equation:

2A(g) + B(g)⇌3C(g)

If the volume of the reaction container is increased at constant tempera-

ture, predict the direction in which the equilibrium will shift and explain your

reasoning.

Solution

Step 1: Determine the effect of increasing volume on the equilibrium system.

When the volume of the reaction container is increased, the pressure inside

the container decreases according to Boyle’s Law, which states that pressure is

inversely proportional to volume at constant temperature.

Step 2: Apply Le Chatelier’s principle to predict the equilibrium shift.

According to Le Chatelier’s principle, a system at equilibrium will respond

to a stress by shifting the equilibrium position in a direction that reduces the

stress. In this case, the stress is the decrease in pressure due to the increase in

volume.

Step 3: Analyze the equilibrium system based on the stoichiometry of the

reaction.

In the given equilibrium reaction, the number of moles of gas molecules on

the left side of the reaction (2 moles of A and 1 mole of B) is greater than the

number of moles of gas molecules on the right side (3 moles of C).

Step 4: Predict the direction of the equilibrium shift.

Since increasing the volume causes a decrease in pressure, the equilibrium

system will shift in the direction that produces more moles of gas molecules to

counteract the decrease in pressure. Therefore, the equilibrium will shift to the

right, towards the side with more moles of gas (the side with 3 moles of C).

Therefore, when the volume of the reaction container is increased at constant

temperature, the equilibrium will shift to the right to counteract the decrease

in pressure caused by the increase in volume.

Question 13

Question

For the reaction:

H2O(l) + Cl2(g)⇌HCl(aq) + HOCl(aq)

which is in equilibrium, predict the effect of each of the following changes on

the equilibrium position (shift to the left, shift to the right, or no change): a)

Addition of more water b) Decrease in temperature c) Addition of a catalyst

Solution

Step 1: For each change, we will analyze how the equilibrium position shifts by

applying Le Chatelier’s principle.

a) Addition of more water: When more water is added, according to Le

Chatelier’s principle, the equilibrium will shift to the side with fewer moles of

gas to decrease the pressure. In this case, the left side of the equation has

fewer moles of gas (1 mole of gas) compared to the right side (2 moles of gas).

Therefore, the equilibrium will shift to the left.

b) Decrease in temperature: If the temperature is decreased, the equilibrium

will shift in the direction that absorbs heat. This can be achieved by considering

the enthalpy change of the reaction. If the reaction is exothermic (negative �H),

then it will shift to the right to produce more heat. If the reaction is endothermic

(positive �H), then it will shift to the left to absorb more heat.

c) Addition of a catalyst: The addition of a catalyst does not affect the

position of equilibrium; it only speeds up the attainment of equilibrium by

lowering the activation energy for the forward and reverse reactions. Therefore,

the addition of a catalyst will have no effect on the equilibrium position.

Question 14

Question

Consider the following equilibrium reaction:

2SO2(g) + O2(g)⇌2SO3(g)

If the concentration of SO2is increased, predict the direction in which the

equilibrium will shift and explain why using Le Chatelier’s principle.

Solution

Step 1: Write the reaction with the changes in concentration:

2SO2(g) + O2(g)⇌2SO3(g)

If the concentration of SO2is increased, the reaction will respond to decrease

the excess SO2and shift the equilibrium to the right.

Step 2: Apply Le Chatelier’s principle:

Increasing the concentration of SO2causes the system to adjust by consum-

ing some of the SO2to establish a new equilibrium. The reaction shifts to the

right to produce more SO3to balance the new concentration of SO2.

Therefore, the equilibrium will shift to the right in response to the increase

in SO2concentration according to Le Chatelier’s principle.

Question 15

Question

For the reaction:

2 SO2(g) + O2(g)⇌2 SO3(g)

Which one of the following changes would shift the equilibrium to the right?

A. Increasing the temperature B. Decreasing the pressure by increasing the

volume C. Adding a catalyst D. Increasing the concentration of SO�

Solution

To shift the given reaction equilibrium to the right, we need to consider Le

Chatelier’s principle.

Step 1: Increasing the temperature When the temperature is increased,

the equilibrium will shift in the endothermic direction to counteract the change.

In this case, the forward reaction is exothermic (producing heat), so increasing

the temperature would shift the equilibrium to the left, not to the right.

Step 2: Decreasing the pressure by increasing the volume According to Le

Chatelier’s principle, if the pressure is decreased, the equilibrium will shift in the

direction with more moles of gas to counteract the change. In this case, both the

reactant and product side have 3 moles of gas, so changing the pressure/volume

would not have an effect on the equilibrium position.

Step 3: Adding a catalyst Adding a catalyst does not shift the position of

equilibrium. It only increases the rate at which equilibrium is reached, without

affecting the ratio of products to reactants.

Step 4: Increasing the concentration of SO� According to Le Chatelier’s

principle, if the concentration of a reactant is increased, the equilibrium will shift

to the right to counteract the change. Therefore, increasing the concentration

of SO2will shift the equilibrium to the right.

Therefore, the correct answer is:

D. Increasing the concentration of SO2

Question 16

Question

A gaseous reaction mixture at equilibrium contains nitrogen dioxide (NO2) and

dinitrogen tetroxide (N2O4) in a sealed container. The equilibrium is repre-

sented by the following reaction:

2NO2(g)⇌N2O4(g)

If the pressure of the system is increased by decreasing the volume of the

container, predict the direction in which the equilibrium will shift. Justify your

answer.

Solution

Step 1: Identify the initial effect of increasing pressure on the equilibrium:

When the pressure of a gaseous system is increased by decreasing the volume,

the system will respond by shifting the equilibrium in the direction that reduces

the total number of moles of gas.

Step 2: Determine the change in the total number of moles of gas for this

reaction:

The reaction is 2NO2(g)⇌N2O4(g). On the reactant side, there are 2

moles of gas (2NO2). On the product side, there is 1 mole of gas (N2O4).

Step 3: Determine the direction of equilibrium shift based on the change in

total moles of gas:

Since there are more moles of gas on the reactant side compared to the

product side, increasing the pressure will cause the equilibrium to shift in the

direction that decreases the total moles of gas. Therefore, the equilibrium will

shift to the left to reduce the total number of gas moles.

Step 4: Justify the direction of equilibrium shift:

Shifting to the left means more N2O4will be formed leading to a decrease in

the moles of gas and thus reducing the pressure to counteract the initial increase

in pressure by the decrease in volume. This shift helps maintain the equilibrium

constant and minimize the effect of the pressure change.

Question 17

Question

For the reaction CO(g) + H2O(g)⇌CO2(g) + H2(g), which of the following

changes would cause an increase in the concentration of H2(g)at equilibrium?

1. Decreasing the volume of the reaction vessel

2. Adding more CO2gas to the reaction mixture

3. Removing some of the CO(g)from the reaction vessel

4. Increasing the temperature of the reaction mixture

Solution

To determine the effect of each change on the concentration of H2(g)at equi-

librium, we must consider the reaction and apply Le Chatelier’s principle.

The given reaction is:

CO(g) + H2O(g)⇌CO2(g) + H2(g)

1. Decreasing the volume of the reaction vessel:

By decreasing the volume of the reaction vessel, the system will respond

by shifting the equilibrium to decrease the total number of gas molecules.

Since H2(g)has fewer moles of gas than CO2(g)or CO(g), the equilibrium

will shift to the right, increasing the concentration of H2(g).

2. Adding more CO2gas to the reaction mixture:

Adding more CO2gas will increase the concentration of a product of the

reaction. According to Le Chatelier’s principle, the equilibrium will shift

to the left to reduce the excess CO2gas, decreasing the concentration of

H2(g)at equilibrium.

3. Removing some of the CO(g)from the reaction vessel:

Removing some of the CO(g)gas will decrease the concentration of a

reactant. To compensate, the equilibrium will shift to the left to produce

more CO(g), consuming some H2(g)in the process. This will decrease the

concentration of H2(g)at equilibrium.

4. Increasing the temperature of the reaction mixture:

Increasing the temperature of the reaction mixture will favor the endother-

mic reaction. In this case, since the forward reaction is endothermic

(∆H > 0, absorbing heat), increasing the temperature will shift the equi-

librium to the right to absorb the excess heat, leading to an increase in

the concentration of H2(g)at equilibrium.

Therefore, the change that would cause an increase in the concentration

of H2(g)at equilibrium is increasing the temperature of the reaction

mixture.

Question 18

Question

For the reaction below at equilibrium, predict how each of the following changes

will affect the concentration of Pfrom the given choices. State whether the

concentration of Pwill increase, decrease, or remain unchanged.

2A(g) + B(g) <=> P(g) + Q(g) + heat

1. Addition of more A at constant volume and temperature.

2. Removal of some A at constant volume and temperature.

3. Addition of an inert gas at constant volume and temperature.

4. Increase in the volume of the system at constant temperature.

Solution

Le Chatelier’s principle states that if a system at equilibrium is subjected to a

stress, the system will adjust so as to relieve the stress and partially offset the

effect of the stress. Let’s analyze each scenario:

1. Addition of more A at constant volume and temperature:

• This change will disturb the equilibrium of the reaction. According

to Le Chatelier’s principle, the system will shift to relieve the stress

by consuming some of the additional A.

• As a result, the concentration of A will decrease, causing the con-

centrations of B, P, and Q to increase to reestablish equilibrium.

Therefore, the concentration of P will increase.

2. Removal of some A at constant volume and temperature:

• Removing some A will disturb the equilibrium. To counteract this

stress, the system will shift to replace the lost A by converting some

P and Q back into A and B.

• Consequently, the concentration of A will increase, leading to a de-

crease in the concentrations of P, Q, and B. Thus, the concentration

of P will decrease.

3. Addition of an inert gas at constant volume and temperature:

• Adding an inert gas will not affect the concentrations of the reactants

or products because an inert gas does not participate in the reaction.

• Therefore, the concentration of P will remain unchanged.

4. Increase in the volume of the system at constant temperature:

• When the volume is increased, the system will shift to the side with

more gaseous moles to compensate for the expansion.

• In this case, the reactants A and B have a total of 3 moles of gas,

while the products P and Q have a total of 2 moles of gas. Thus, the

system will shift to the left to increase the total gas moles, favoring

the reactants.

• As a result, the concentrations of P and Q will decrease, causing the

concentration of P to decrease.

Question 19

Question

For the reaction below at equilibrium, which of the following changes will shift

the equilibrium to the right, increasing the concentration of product B?

A(g) + 2B(g) <=> C(g)

A. Increasing the volume of the container

B. Adding more of substance A

C. Decreasing the pressure by increasing the volume of the container

D. Removing some of substance B

Solution

To determine which changes will shift the equilibrium to the right, increasing

the concentration of product B, we must consider Le Chatelier’s principle.

Step 1: Increasing the volume of the container will shift the equilibrium to

the side with more gas molecules to decrease the pressure. Since there are 3

moles of gas on the left side (2 moles of B and 1 mole of A) and 1 mole of gas

on the right side, increasing the volume of the container will shift the equilib-

rium to the left, increasing the concentration of substance A and decreasing the

concentration of product B. Therefore, increasing the volume of the container

will not increase the concentration of product B.

Step 2: Adding more of substance A will increase the concentration of

substance A and shift the equilibrium to the side with fewer moles of A to relieve

the stress. Since substance A is on the left side, adding more A will shift the

equilibrium to the right, increasing the concentration of product B. Therefore,

adding more of substance A will increase the concentration of product B.

Step 3: Decreasing the pressure by increasing the volume of the container

will shift the equilibrium to the side with more moles of gas to increase the

pressure. Since there are 3 moles of gas on the left side and 1 mole of gas on the

right side, decreasing the pressure by increasing the volume of the container will

shift the equilibrium to the left, increasing the concentration of substance A and

decreasing the concentration of product B. Therefore, decreasing the pressure

by increasing the volume of the container will not increase the concentration of

product B.

Step 4: Removing some of substance B will decrease the concentration of

substance B and shift the equilibrium to the side with more B to relieve the

stress. Since substance B is on the right side, removing some B will shift the

equilibrium to the right, increasing the concentration of product B. Therefore,

removing some of substance B will increase the concentration of product B.

Therefore, the correct answer is B. Adding more of substance A and D.

Removing some of substance B will both shift the equilibrium to the right,

increasing the concentration of product B.

Question 20

Question

A reaction vessel initially contains 0.1 M of NOCl(g) at equilibrium with NO(g)

and Cl2(g), according to the equation:

2NOCl(g)⇌2NO(g) + Cl2(g)

Determine the effect of the following changes on the equilibrium position

(shift left, shift right, or no effect) at constant temperature:

(a) Addition of NO(g) to the reaction vessel (b) Reduction of the volume of

the reaction vessel (c) Increase in the temperature of the reaction vessel

Solution

Step 1: Write the equilibrium expression based on the given equation:

K=[NO]2[Cl2]

[NOCl]2

Step 2: Analyze the effects of each change on the equilibrium position:

(a) Addition of NO(g) to the reaction vessel: - According to Le Chatelier’s

principle, adding more NO(g) will shift the equilibrium to the left to consume the

extra NO(g) by forming more NOCl(g). - This will decrease the concentrations

of NO and Cl2, and increase the concentration of NOCl.

Therefore, the equilibrium position will shift to the left.

(b) Reduction of the volume of the reaction vessel: - Decreasing the volume

will increase the pressure inside the vessel. - Since there are more gas molecules

on the right side of the equation, the equilibrium will shift to the side with fewer

gas molecules to decrease the pressure. - This means the equilibrium will shift

to the left to reduce the total number of gas molecules.

Therefore, the equilibrium position will shift to the left.

perature will favor the endothermic reaction to absorb the excess heat. - Since

the reaction is endothermic (heat on the reactant side), the equilibrium will

shift to the right to consume the excess heat.

Therefore, the equilibrium position will shift to the right.

Question 21

Question

Consider the following equilibrium reaction:

2NOCl(g)⇌2NO(g) + Cl2(g)

If the equilibrium constant, Kc, for this reaction at a certain temperature is

found to be 0.25, what can be said about the reaction quotient, Qc, for the

system at the following cases: a) Qc= 0.1b) Qc= 0.25 c) Qc= 0.5

Solution

Step 1: Recall the formula for the reaction quotient:

Qc=[NO]2[Cl2]

[NOCl]2

Step 2: Compare the reaction quotient, Qc, with the equilibrium constant,

Kc, to determine the direction of the reaction shift. a) If Qc< Kc, the reaction

will shift to the right to reach equilibrium. b) If Qc=Kc, the system is at

equilibrium. c) If Qc> Kc, the reaction will shift to the left to reach equilibrium.

Step 3: a) For Qc= 0.1< Kc= 0.25, the reaction will shift to the right to

reach equilibrium. b) For Qc=Kc= 0.25, the system is at equilibrium. c) For

Qc= 0.5> Kc= 0.25, the reaction will shift to the left to reach equilibrium.

Question 22

Question

Given the following equilibrium reaction:

2 SO2(g) + O2(g)⇌2 SO3(g)

If the volume of the container is increased, predict the direction in which

the equilibrium will shift. Justify your answer with Le Chatelier’s Principle.

Solution

Step 1: Write the balanced equilibrium equation. The balanced equilib-

rium equation is:

2 SO2(g) + O2(g)⇌2 SO3(g)

Step 2: Analyze the effects of increasing volume on the equilibrium

system. When the volume of the container is increased, the system will try to

counteract the change to minimize the effect of the volume change.

Step 3: Apply Le Chatelier’s Principle. - If the volume of the container

is increased, the system will shift towards the side with more moles of gas to

minimize the effect of the volume change. - In this reaction, there are 3 moles of

gas on the left side (2 moles of SO� and 1 mole of O�) and 2 moles of gas on the

right side (2 moles of SO�). - Therefore, increasing the volume will cause the

equilibrium to shift to the right to decrease the total gas volume and increase

the pressure inside the container.

Step 4: Conclusion. Increasing the volume of the container will cause

the equilibrium to shift towards the formation of more products, in this case,

towards the formation of more SO�.

Question 23

Question

For the reaction:

N2O4(g)⇌2NO2(g)

What will happen to the equilibrium position if the volume of the reaction

vessel is decreased?

Solution

Step 1: Write the balanced chemical equation.

The balanced chemical equation for the reaction is:

N2O4(g)⇌2NO2(g)

Step 2: Determine the effect of decreasing the volume on the equilibrium.

According to Le Chatelier’s principle, if the volume of the reaction vessel is

decreased, the system will respond in a way that tends to counteract the change.

Step 3: Determine the change in volume affects the equilibrium position.

Decreasing the volume of the reaction vessel will increase the pressure inside

the vessel. Since there are 2 moles of gas on the right side of the reaction and

only 1 mole of gas on the left side, the reaction will shift towards the side with

fewer moles of gas to decrease the pressure.

Step 4: Determine the shift in equilibrium.

Therefore, decreasing the volume will cause the equilibrium to shift to the

left, resulting in an increase in the concentration of N2O4and a decrease in the

concentration of NO2.

Step 5: Conclusion

In conclusion, if the volume of the reaction vessel is decreased, the equilib-

rium position will shift to the left, favoring the formation of N2O4and decreasing

the concentration of NO2gas.

Question 24

Question

Consider the following equilibrium reaction:

2 NOBr(g)⇌2 NO(g) + Br2(g)

Which of the following changes would lead to an increase in the concentration

of NOBr at equilibrium? Choose all that apply. i) Increasing the pressure by

decreasing the volume of the container. ii) Increasing the temperature of the

system. iii) Removing some NO from the system. iv) Adding an inert gas at

constant volume.

Solution

Step 1: Recall Le Chatelier’s Principle. When a system at equilibrium is dis-

turbed by a change in temperature, pressure, or concentration of one of the

components, the system will shift its position of equilibrium to counteract the

effect of the disturbance.

Step 2: For the given reaction, an increase in the concentration of NOBr

at equilibrium indicates a shift to the left side of the reaction (towards the

reactants).

Step 3: Let’s consider each option: i) Increasing the pressure by decreasing

the volume of the container will shift the equilibrium towards the side with fewer

moles of gas molecules. In this case, the left side has 3 moles of gas molecules

(2 NOBr) and the right side has 2 moles (2 NO + Br2). Therefore, decreasing

the volume will push the equilibrium to the left, increasing the concentration of

NOBr. This statement is true. ii) Increasing the temperature of the system will

favor the endothermic direction to absorb the additional heat. This means the

equilibrium will shift to the right, reducing the concentration of NOBr. This

statement is false. iii) Removing some NO from the system would decrease the

concentration of NO, which would disturb the equilibrium. To counteract this

change, the equilibrium will shift to the left, increasing the concentration of

NOBr. This statement is true. iv) Adding an inert gas at constant volume does

not affect the concentrations of the reactants or products. This statement is

false.

Step 4: Therefore, the correct answers are: i) Increasing the pressure by

decreasing the volume of the container. iii) Removing some NO from the system.

Question 25

Question

A reaction is at equilibrium with the following equilibrium equation:

2A(g) + B(g) ⇌C(g)

If the volume of the reaction vessel is increased, predict the direction in

which the equilibrium will shift and explain why using Le Chatelier’s principle.

Solution

Step 1: According to Le Chatelier’s principle, when a change is imposed on a

system at equilibrium, the position of equilibrium will shift in a direction that

tends to counteract the change.

Step 2: Increasing the volume of the reaction vessel will decrease the overall

pressure inside the vessel.

Step 3: In this case, the reaction involves gas-phase components only. When

pressure is decreased, the equilibrium will shift towards the side with more moles

of gas in order to increase the pressure back towards its original value.

Step 4: Since the reactants (2 moles of A and 1 mole of B) have a total of

3 moles of gas, while the product (1 mole of C) has only 1 mole of gas, the

equilibrium will shift towards the reactants to offset the decrease in pressure.

Step 5: Therefore, increasing the volume of the reaction vessel will cause the

equilibrium to shift towards the left, favoring the formation of more A(g) and

B(g) from C(g).

Question 2

Question

For the reaction N2O4(g)⇌2NO2(g)at equilibrium, ∆H= +57.2kJ.

If the equilibrium constant Kc= 0.82 at 25◦C, how will the equilibrium shift

when the temperature is increased? Justify your answer.

Solution

Step 1: Given data. The equation for the reaction is: N2O4(g)⇌2NO2(g)

∆H= +57.2kJ (endothermic reaction)

Kc= 0.82 at 25◦C

Step 2: Le Chatelier’s Principle When the temperature is increased in an

endothermic reaction, the equilibrium will shift towards the products side to

absorb the added heat.

Step 3: Justification Since the reaction is endothermic, increasing the tem-

perature will favor the endothermic reaction to absorb the excess heat. The

equilibrium will shift towards the products side (2NO2) to counteract the in-

crease in temperature.

Therefore, the equilibrium will shift to the right (towards the products) when

the temperature is increased.

Question 3

Question

For the reaction:

H2O(g)⇌2H2O(l)

What effect would each of the following changes have on the position of the

equilibrium (shift to the left, shift to the right, or no change)? Justify your

answers.

(a) Increasing the pressure by decreasing the volume of the container.

(b) Adding a catalyst to the reaction vessel.

(d) Increasing the temperature of the reaction vessel.

Solution

(a) Increasing the pressure by decreasing the volume of the container:

•Step 1: According to Le Chatelier’s principle, increasing the pressure on

a system at equilibrium will cause the equilibrium to shift in the direction

that reduces the total number of gas moles.

•Step 2: In this case, the reaction involves the conversion of gaseous water

to liquid water, so decreasing the volume (increasing pressure) will shift the

equilibrium to the right to reduce the pressure by decreasing the amount

of gaseous water.

•Step 3: Therefore, increasing the pressure by decreasing the volume of

the container will shift the equilibrium to the right.

(b) Adding a catalyst to the reaction vessel:

•Step 1: A catalyst does not affect the position of the equilibrium. It only

speeds up the rate at which equilibrium is reached but does not change

the position of the equilibrium.

•Step 2: Therefore, adding a catalyst to the reaction vessel will have no

effect on the position of the equilibrium.

•Step 1: According to Le Chatelier’s principle, if a reactant or product

is removed from a system at equilibrium, the equilibrium will shift in the

direction to replace the substance that was removed.

•Step 2: In this case, liquid water is being removed, which is a product of

the reaction. Therefore, the equilibrium will shift to the left in order to

produce more liquid water.

•Step 3: Removing some of the liquid water from the reaction vessel will

shift the equilibrium to the left.

(d) Increasing the temperature of the reaction vessel:

•Step 1: When the temperature of a system at equilibrium is changed,

the equilibrium will shift in the direction that absorbs or releases heat in

order to counteract the change in temperature.

•Step 2: In this case, the reaction is endothermic (heat is a reactant).

Increasing the temperature will favor the endothermic reaction to absorb

the added heat, so the equilibrium will shift to the right.

•Step 3: Therefore, increasing the temperature of the reaction vessel will

shift the equilibrium to the right.

Question 4

Question

For the reaction:

2 NO2(g)⇌2 NO(g) +O2(g)

Which gas will cause an increase in the concentration of NO2at equilibrium?

Justify your answer using Le Chatelier’s principle.

Solution

Step 1: According to Le Chatelier’s principle, if a stress is applied to a system at

equilibrium, the system will respond by shifting the equilibrium to counteract

the stress.

Step 2: In this reaction, the concentration of NO2can be increased by either

increasing the concentration of NO or O2.

Step 3: Increasing the concentration of O2will shift the equilibrium to the

left, favoring the formation of NO2.

Step 4: Thus, increasing the concentration of O2will cause an increase in

the concentration of NO2at equilibrium.

Therefore, the gas that will cause an increase in the concentration of NO2

at equilibrium is O2.

Question 5

Question

Consider the following reaction at equilibrium:

2 SO2(g) + O2(g)⇌2 SO3(g)

If the pressure of the system is increased by decreasing the volume, predict

the direction in which the equilibrium will shift. Justify your answer using Le

Chatelier’s principle.

Solution

Step 1: Identify the effect of decreasing volume on the system.

Decreasing the volume of the system will increase the overall pressure within

the system.

Step 2: Apply Le Chatelier’s principle. - In this reaction, the increase in

pressure from a decreased volume will shift the equilibrium to counteract the

increase in pressure. - According to Le Chatelier’s principle, the system will

respond by favoring the side of the reaction with fewer gas moles to decrease

the pressure.

Step 3: Analyze the reaction. - On the reactant side, there are 3 moles of

gas (2 moles of SO2 and 1 mole of O2). - On the product side, there are 2 moles

of gas (2 moles of SO3).

Step 4: Determine the direction of the equilibrium shift. - Since the reactant

side has more gas moles, the equilibrium will shift to the left to decrease the

pressure by consuming some of the gas-phase reactants.

Therefore, if the pressure of the system is increased by decreasing the volume,

the equilibrium will shift to the left to relieve the pressure increase.

This shift to the left will result in an increase in the concentrations of SO2

and O2 and a decrease in the concentration of SO3 until a new equilibrium is

established.

Question 6

Question

In an aqueous solution, the reaction 2 HgCl2(aq)⇌2 Hg(s) + Cl2(g)is estab-

lished at equilibrium. If the volume of the container is suddenly decreased, pre-

dict how the equilibrium will shift according to Le Chatelier’s principle. Justify

your answer.

Solution

Step 1: Identify the factors that can affect the equilibrium: The factors to

consider include concentration, temperature, and volume changes.

Step 2: Analyze the effect of decreasing the volume on the system: When

the volume of the container is decreased, the system will try to counteract this

change by shifting the equilibrium to reduce the pressure.

Step 3: Determine the side of the reaction that has fewer gas molecules: On

the reactant side, there are 2 moles of gas (all in the form of Cl2gas), while on

the product side, there is only 1 mole of gas (the Cl2gas).

Step 4: Predict the direction of the equilibrium shift: Since decreasing the

volume increases the pressure, the system will shift the equilibrium to the side

with fewer gas molecules to alleviate some of the increased pressure. Therefore,

the equilibrium will shift to the right (towards the products) to decrease the

total number of gas molecules.

Step 5: Justify the answer: The reaction will proceed in the direction that

will decrease the total number of gas molecules to counteract the increased

pressure due to the decrease in volume. Thus, the equilibrium will shift towards

the products (Hg and Cl2) to establish a new equilibrium position with a lower

total gas pressure.

Question 7

Question

Consider the following equilibrium reaction:

2SO2(g) + O2(g)⇌2SO3(g)

At a certain temperature, the equilibrium constant, Kc, for this reaction is

0.56. If a reaction vessel initially contains 0.50 M of SO2, 0.25 M of O2, and 0.20

M of SO3, what will be the change in each of the concentrations at equilibrium?

Solution

Step 1: Let’s define the initial concentrations and changes in concentration as

follows: - Let xbe the change in concentration for both SO2and O2(since they

both decrease) and 2xbe the change in concentration for SO3(since it increases

by a factor of 2). - The initial concentrations are:

[SO2]initial = 0.50 M

[O2]initial = 0.25 M

[SO3]initial = 0.20 M

Step 2: Using the information above, we can set up an ICE (initial, change,

equilibrium) table for the reaction:

Compound Equation [Compound]initial Change [Compound]equilibrium

SO22SO2(g) + O2(g)⇌2SO3(g) 0.50 −x0.50 −x

O22SO2(g) + O2(g)⇌2SO3(g) 0.25 −x0.25 −x

SO32SO2(g) + O2(g)⇌2SO3(g) 0.20 +2x0.20 + 2x

Step 3: Now, we can write the expression for the equilibrium constant, Kc,

in terms of the concentrations at equilibrium:

Kc=[SO3]2

[SO2]2[O2]= 0.56

Substitute the equilibrium concentrations into the equation above and solve

for x.

Step 4: Once you have found the value of x, you can calculate the equilibrium

concentrations for each compound. Subsitute the value of xinto the expressions

derived in the ICE table.

Therefore, the change in each of the concentrations at equilibrium can be

determined.

Question 8

Question

For the reaction

N2O4(g)⇌2NO2(g)

at a certain temperature, the equilibrium constant Kcis 0.42. If the concen-

tration of N2O4at equilibrium is 0.25 M, what is the concentration of NO2at

equilibrium?

Solution

Step 1: Write the equilibrium expression for the reaction:

Kc=[NO2]2

[N2O4]

Step 2: Given that Kc= 0.42 and [N2O4] = 0.25 M, we can rearrange the

equilibrium expression to solve for [NO2]:

0.42 = [NO2]2

0.25

Step 3: Solve for [NO2]:

[NO2]2= 0.42 ×0.25

[NO2]2= 0.105

Step 4: Take the square root of both sides to find [NO2]:

[NO2] = √0.105

[NO2]≈0.324 M

Therefore, the concentration of NO2at equilibrium is approximately 0.324

Question 9

Question

A gaseous equilibrium is established according to the reaction:

N2(g)+3H2(g)⇌2NH3(g)

If the pressure of N2is decreased at constant temperature, predict in which

direction the equilibrium will shift. Justify your answer.

Solution

Step 1: Determine the effect of decreasing the pressure of N2. According to Le

Chatelier’s principle, decreasing the pressure of a system will cause the equilib-

rium to shift in the direction that produces more moles of gas to compensate

for the pressure change.

Step 2: Examine the stoichiometry of the reaction. On the reactant side,

there are 1 mole of N2and 3 moles of H2, totaling 4 moles of gas. On the

product side, there are 2 moles of NH3. Therefore, the forward reaction (to the

right) produces more moles of gas.

Step 3: Conclusion. Since decreasing the pressure of N2will shift the equi-

librium towards the direction that produces more moles of gas, the equilibrium

will shift to the right (towards the products) to increase the total gas moles and

alleviate the pressure decrease.

Question 10

Question

Consider the following reaction at equilibrium:

2 HgCl2(aq)⇌2 Hg(s) + 2 Cl−(aq)

If additional solid Hg is added to the system at constant temperature and

pressure, predict how the equilibrium will shift. Justify your answer using Le

Chatelier’s principle.

Solution

Step 1: The addition of solid Hg will cause the reaction to shift towards the

reactants in order to counteract the increase in the concentration of Hg.

Step 2: According to Le Chatelier’s principle, an increase in the concen-

tration of a reactant will cause the equilibrium to shift in the direction that

consumes that reactant.

Step 3: In this case, the reaction consumes Hg to form HgCl2, so the equi-

librium will shift to the left to produce more HgCl2.

Step 4: As a result, additional solid Hg will cause the equilibrium to shift to

the left, favoring the formation of more HgCl2attheexpenseofHg.

Step 5: Thus, the equilibrium will shift to the left when additional solid

Hg is added to the system at constant temperature and pressure in order to

maintain equilibrium.

Question 11

Question

For the reaction CO(g) + H2O(g)⇌CO2(g) + H2(g), which will result in an

increase in the equilibrium constant if the pressure is increased?

Solution

Step 1: First, let’s determine the change in moles of gas when the reaction shifts

towards the products in response to an increase in pressure. Since one mole of

CO and one mole of H2O will result in two moles of gas, and one mole of CO2

and one mole of H2 will only result in two moles of gas as well, the total change

is 0 moles of gas. Therefore, the reaction will not shift towards the products in

response to an increase in pressure.

Step 2: According to Le Chatelier’s Principle, if the pressure is increased and

the reaction does not shift towards the products, then the system must try to

counteract the change in pressure by shifting in the opposite direction. In this

case, the system will shift towards the reactants when the pressure is increased.

Step 3: Since the reaction shifts towards the reactants in response to an

increase in pressure, the concentration of CO and H2O will increase, while the

concentration of CO2 and H2 will decrease. This will result in an increase in

the numerator and a decrease in the denominator of the equilibrium constant

expression, ultimately leading to an increase in the equilibrium constant.

Therefore, the equilibrium constant will increase if the pressure is increased

for the reaction CO(g) + H2O(g)⇌CO2(g) + H2(g).

Question 12

Question

A gaseous equilibrium system is described by the equation:

2A(g) + B(g)⇌3C(g)

If the volume of the reaction container is increased at constant tempera-

ture, predict the direction in which the equilibrium will shift and explain your

reasoning.

Solution

Step 1: Determine the effect of increasing volume on the equilibrium system.

When the volume of the reaction container is increased, the pressure inside

the container decreases according to Boyle’s Law, which states that pressure is

inversely proportional to volume at constant temperature.

Step 2: Apply Le Chatelier’s principle to predict the equilibrium shift.

According to Le Chatelier’s principle, a system at equilibrium will respond

to a stress by shifting the equilibrium position in a direction that reduces the

stress. In this case, the stress is the decrease in pressure due to the increase in

volume.

Step 3: Analyze the equilibrium system based on the stoichiometry of the

reaction.

In the given equilibrium reaction, the number of moles of gas molecules on

the left side of the reaction (2 moles of A and 1 mole of B) is greater than the

number of moles of gas molecules on the right side (3 moles of C).

Step 4: Predict the direction of the equilibrium shift.

Since increasing the volume causes a decrease in pressure, the equilibrium

system will shift in the direction that produces more moles of gas molecules to

counteract the decrease in pressure. Therefore, the equilibrium will shift to the

right, towards the side with more moles of gas (the side with 3 moles of C).

Therefore, when the volume of the reaction container is increased at constant

temperature, the equilibrium will shift to the right to counteract the decrease

in pressure caused by the increase in volume.