Quiz for chemistry
Spontaneous Process
1. Proceeds without assistance, and the reverse is nonspontaneous.
2. Phase Change is spontaneous when T> 0 or when T< 0.
Thermodynamics
1. Extent of reaction
2. Nothing about the rate of reaction
a. Vocabulary
i. System: the part of the world that we are considering
1. Open system: both matter and heat can flow in or out
2. Closed system: heat can flow in or out, but not matter
3. Isolated system: neither eat or matter can flow in or out
ii. Surroundings: The part of the world immediately around the system
Reversible vs. Irreversible
3. The carrot engine: max efficiency (ideal)
4. Reversible can be restored to the original state with no net change and produces
maximum work.
Ideal gas expansion: isothermal process
Reversible or Not?
1. Reversible occurring infinitely slowly and with no change to the surroundings.
2. Spontaneous processes: All reversible
Entropy and the 2 law of thermodynamics
nd
1. Entropy: the extent of randomness
2. Calculated: Delta S = S(final)- S(initial)
3. In isothermal reversible: Delta S = qrev/T (kelvin)
4. Entropy is a measure of how many possible arrangements can give rise to the same state
of a system
5. The first law of thermodynamics: energy is conserved
6. The second law of thermodynamics: entropy increases for spontaneous processes
Refining the statement
1. Total entropy increases for irreversible processes
2. Total entropy is unchanged for reversible processes
Molecular Interpretation
1. Ludwig Boltzmann: microstates (number of arrangements= W) and probability
2. Delta S = k ln (W final/ W initial)
3. He put S= k log W on his tombstone
Molecular Motion and Energy
1. Increasing temperature increases movement and so, the microstates
2. Types of motions: translation, rotation, and vibration
3. The number of possible microstates and, therefore the entropy tends to increase with
increases in
a. Temperature
b. Volume
c. The number of independently moving molecules
4. Entropy increases with the freedom of motion of molecules
a. S(g) > S(l) > S(s)
Third Law of Thermodynamics
1. At 0 K the entropy of a pure crystalline solid is 0
Entropy Changes in Chemical Reactions
1. Entropy can be absolutely determined
2. Varies with temperature and jumps with phase change
Molar Entropies S
1. Non-Zero
2. Gases > liquids and solids
3. Increasing with molar mass
4. Increase with Number of atoms in the formula.
Gibbs Free Energy
1. Accounts for both entropy and enthalpy
2. G= H- T(S)
3. Delta G = Delta H – ( T )(Delta S)
4. Spontaneous means delta G < 0
5. Note that the higher the T, the more that S contributes and the lower the T the more that
H contributes
What is Free about Free Energy?
1. Reversible vs. Irreversible...
2. G is the maximum useful work by the system, the portion “free” to do useful work G
= -wmax
3. For nonspontaneous processes, it is the minimum amount of work that must be done to
cause the process.
Signs
If H is -, exothermic
If H is +, endothermic
If S is -, entropy decreases (system more ordered)
If S is +, entropy increases (system less ordered)
Two important circumstances:
1. All of the concentrations are equal to “1”.
2. Concentrations are equal to the equilibrium values.
