Untitled - Kelly Walsh High School

262 CHEMISTRY FOR THE UTTERLY CONFUSED
related to the disorder of the system. Entropy increases when the number of
molecules increases, with an increase in temperature, when a gas forms from a
solid or liquid or when a liquid forms from a solid. Gibbs free energy is the best
indicator of a spontaneous reaction. If ∆G > 0, the reaction is not spontaneous;
if ∆G < 0, the reaction is spontaneous; and if ∆G 0, the reaction is at equilibrium.
It is possible to use the ∆G and the temperature to calculate the equilibrium
constant of a reaction.
1. State the first, second, and third laws of thermodynamics.
2. Which of the following involves an increase in entropy?
a. a solid melting b. a liquid freezing c. a gas condensing
d. two gases reacting to produce a solid product
e. a gas changing to a solid (undergoing deposition)
3. The Gibbs free energy for a spontaneous process has a _____ sign.
4. What is the mathematical definition of Gibbs free energy?
5. How can a process where ∆S system is negative ever be spontaneous?
6. What are standard conditions?
7. What is the mathematical relationship necessary to adjust the Gibbs free
energy to nonstandard conditions.
8. What is the mathematical relationship that relates the Gibbs free energy to
the equilibrium constant.
9. What is the value of R used in thermochemical relationships?
10. How are K and Q similar? How are K and Q different?
11. What do the ∆H f and ∆G f values for elements have in common?
12. Determine the change in the standard entropy for the following reaction:
Ca(s) S(s) 3 O 2(g) 2 H 2(g) l CaSO 42H 2O(s)
The S° values are
Ca(s) 41.63 J/molK S(s) 31.88 J/molK O 2(g) 205.0 J/molK
H 2(g) 131.0 J/molK CaSO 42H 2O(s) 194.0 J/molK
13. Determine the change in the standard Gibbs free energy for the following
reaction:
Ca(s) 2 H 2SO 4(l) l CaSO 4(s) SO 2(g) 2 H 2O(l)
The ∆G f values are
Ca(s) 0.00 kJ/mol H 2SO 4(l) 689.9 kJ/mol SO 2(g) 300.4 kJ/mol
H 2O(l) 237.2 kJ/mol CaSO 4(s) 1320.3 kJ/mol
14. Determine the boiling point of acetone given that the heat of vaporization
is 31.9 kJ/mol and the entropy of vaporization is 96.8 J/molK.
15. Estimate ∆G° for the following equilibrium:
Ag 2CrO 4(s) K 2 Ag (aq) CrO 4 2 (aq) K 1.9 10 16
16. For the following reaction:
C(s) CO 2(g) l 2 CO(g) ∆G° 120.0 kJ.
If 25.00 g of carbon, 2.50 atm of CO and 1.50 atm of CO 2 are placed in a 5.00
L container, calculate G at 25°C.