reading guide 5
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CHEM1212Module5.docxName: __________ _________________________
CHEM 1212 Module 5 Reading Guide
Reaction Rates
A _________ is a measure of how some property varies with time. The rate of a chemical reaction, is defined as the change in the _________ of a reactant or product per unit _________ . Reaction rates are determined by measuring the time dependence of some property that can be related to reactant or product amounts, such as light absorption or conductivity.
There are five factors that can alter the rate of a reaction: (1) the particle _________ of solid reactants, (2) the _________ of reactants, (3) the temperature, (4) the nature of the reactants, and (5) the presence of a _________ . When reactants are in different physical phases, the reaction takes place only at the interface between the phases. Compared with the reaction rate for large solid particles, the rate for smaller particles will be _________ because the surface area in contact with the other reactant phase is _________ .
During a reaction, the reactant atoms, molecules, or ions must come in contact or _________ with each other with enough energy for chemical bond _________ to occur. When you increase the concentration (or for solids, the surface area), you make it _________ likely that particles will collide with each other. The rates of reactions _________ over time as the reactant concentration decreases.
All reactions require a certain amount of _________ to initiate the rearrangement of chemical bonds, regardless of whether the reaction is overall endothermic or _________ . Increasing the _________ of the reaction will increase the _________ energy of the reactant molecules and increase the rate of all reactions. Adding a catalyst allows reactions to happen more _________ at lower temperatures because it lowers the energy cost of the reaction.
The mathematical representation of the change in species concentration over time is the rate expression for the reaction.
For any given reaction, rate expressions are related to one another according to the reaction _________ .
Practice Problems
2. State whether the following changes will result in an increase in the reaction rate, a decrease in the reaction rate, or whether the reaction rate will be unaffected.
a. decreasing the surface area of a reactant
b. decreasing the concentration of a product
c. increasing the temperature
d. adding a catalyst
5. For the reaction 3 A + B → 2 C + 2 D, the rate of change of reactant A is determined to be −3.56×10−3 M⋅s−1.
a. What is the rate of the reaction at this point?
b. What is the rate of change of reactant B?
c. What is the rate of change of product D?
Rate laws
Reaction rates can be measured as _________ or instantaneous rates. Instantaneous rates that are measured close to the start of a reaction are called _________ rates.
Rate laws are _________ determined, mathematical relationships that describe the relationship between the reaction rate and the concentrations of the reactants and are not reliably predicted by reaction _________ .
The generic reaction,
gives a rate law of
Where k, n, and m must be determined _________ . Note that the coefficients of the balanced equation do not appear in the rate law, only in the rate expression. Reaction orders are determined by carefully measuring a reaction’s _________ rate at different _________ of the reactant, while keeping all other conditions unchanged. n is the order with respect to A, and m is the order with respect to B. Common reaction orders are 0, 1, and 2. Negative and _________ orders are possible but less common. The order of the _________ reaction is n + m, the sum of the orders with respect to each reactant.
Rate constants are specific for a particular reaction at a particular _________ . The rate constant is independent of the reactant _________ . The units of the rate constant depend upon the _________ reaction order. Once the reaction orders are determined, you can calculate the rate constant.
Practice Problems
12. The reaction 2 A + 3 B → products has a rate law rate = k[A]2[B].
a. What is the order of the reaction with respect to A?
b. What is the order of the reaction with respect to B?
c. What is the overall reaction order?
14. Consider the initial rate data at a certain temperature for the reaction
2NO(g) + 2H2(g) → N2(g) + 2H2O(g)
|
Experiment |
[H2] (M) |
[NO] (M) |
Initial rate (M/s) |
|
1 |
0.200 |
0.200 |
2.06×10−4 |
|
2 |
0.200 |
0.400 |
8.24×10−4 |
|
3 |
0.400 |
0.400 |
1.65×10−3 |
a. Determine the rate law for the reaction.
b. Calculate the rate constant.
Integrated rate laws
We can determine a second form of each rate law that relates the concentrations of reactants and _________ . These are called _________ rate laws. We can use an integrated rate law to determine the amount of reactant or product present after a period of time or to estimate the _________ required for a reaction to proceed to a certain extent.
The half-life, t1/2, of a reaction is the time it takes for _________ of the reactant to be used up.
For first-order reactions, the half-life is _________ and is _________ of the initial concentration of the reactant. The half-life of a first-order reaction depends on only the _________ and is inversely proportional to the rate constant.
Reaction order and the value of the rate constant can be determined graphically using the integrated rate laws.
Practice Problems
21. The decomposition of sulfuryl chloride, SO2Cl2, is a first-order process with a rate constant of 4.50 × 10-2 s-1 at 660 K.
SO2Cl2(g)→SO2(g)+Cl2(g)
The initial concentration of SO2Cl2 is 0.693 M.
a. Calculate the concentration of SO2Cl2 after 24.5 s.
b. How many seconds does it take for the concentration of SO2Cl2 to drop to
3.59 × 10-3 M?
25. A first-order reaction has a rate constant of 4.38 × 10-4 s-1 at a certain temperature. Calculate the half-life for this reaction in minutes.
Text segments from OpenStax, Chemistry. OpenStax CNX. Sep 15, 2020 http://cnx.org/contents/[email protected].; White, J. et al. Interactive General Chemistry. MacMillan, NY. 2019.; Chemistry LibreTexts, Libretexts, [online] Available from: https://chem.libretexts.org/ Reading guide style Adapted from "Ionic equations Study Guide" by Montgomery College is licensed under CC BY 4.0 Document not to be reposted on the internet without express permission.
