Thermodynamics Classwork
1.
a.
b.
c.
d.
A gas absorbs 28.5J of heat and then performs 15.2 J of work. The change in internal energy of the gas is:
-13.3 J
+13.3 J
-43.7 J
+43.7 J
2. Which of the following statements correctly describes the signs of q and w for the following exothermic
process at 1 atmosphere pressure and 370 Kelvin?
H2O(g)  H2O(l)
a. q and w are both negative
b. q is positive and w is negative
c. q is negative and w is positive
d. q and w are both positive
e. q and w are both zero.
3. A system does 130.J of work on its surroundings while 70.J of heat are added to the system. What is the
internal energy change for the system?
∆E = q + w = -70J + 130J = -60J
4. For the following reactions, performed at constant external pressure, is work done on the system by the
surroundings, by the surrounds on the system or is the amount of work negligible?
a. Sn(s) + 2F2(g)  SnF4(s)
b. AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq)
c. C(s) + O2(g)  CO2(g)
d. SiI4(g) + heat  Si(s) + 2I2(g)
5. The specific heat of Al is 0.89 J/go C. How much energy is required to raise the temperature of a 15.0 g
sample of Al by 18o C?
6. A 5.037 gram piece of iron heated to 100.o C is placed in a calorimeter that initially contains 27.3 g of water
at 21.2o C. If the final temperature is 22.7o C, what is the specific heat capacity of the iron?
7. If 596 J of heat are added to 29.6 g of water at 22.9o C in a calorimeter, what will be the final temperature of
the water? [sp. heat of water = 4.18 J/g o C]
8. Calculate H for the reaction: C2H4 (g) + H2 (g) C2H6 (g), from the following data.
C2H4 (g) + 3 O2 (g) 2 CO2 (g) + 2 H2O (l)
H = -1411. kJ
C2H6 (g) + 3½ O2 (g) 2 CO2 (g) + 3 H2O (l)
H = -1560. kJ
H2 (g) + ½ O2 (g) H2O (l)
H = -285.8 kJ
9. Calculate H for the reaction CH4 (g) + NH3 (g) HCN (g) + 3 H2 (g), given:
N2 (g) + 3 H2 (g) 2 NH3 (g)
H = -91.8 kJ
C (s) + 2 H2 (g) CH4 (g)
H = -74.9 kJ
H2 (g) + 2 C (s) + N2 (g) 2 HCN (g)
H = +270.3 kJ
Bond Energies
C—H
414 kJ/mol
O==O
502 kJ/mol
C==O
730 kJ/mol
O—H
464 kJ/mol
H—H
435 kJ/mol
Cl—Cl
243 kJ/mol
H—Cl
431 kJ/mol
C—Cl
331 kJ/mol
How much energy is absorbed or released (identify which) when each of the following reactions
takes place? Use stoichiometric amounts in each case (e.g. 1.0 mol of CH4 and 2.0 mol of O2 for
problem #1)
10.
CH4 (g) + 2 O2 (g)  CO2 (g) + 2 H2O (g)
11.
2 H2 (g) + O2 (g)  2 H2O (g)
12.
H2 (g) + Cl2 (g)  2 HCl (g)
13. CH4 (g) + Cl2 (g)  CH3Cl (g) + HCl (g)
14. Which one of the following pairs of samples has the higher entropy?
a.
Br2(l) or Br2(g)
b.
C2H6(g) or C3H8(g)
c.
MgO(s) or NaCl(s)
d.
KOH(s) or KOH(aq)
15.
Predict the entropy change for the following processes:
a.
O2(g)  2O(g)
b.
2O3(g)  3O2(g)
c.
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
d.
NaCl(s)  Na+(aq) + Cl-(aq)
e.
C2H5OH(l)  C2H5OH(g)
f.
Ag+(aq) + Cl-(aq)  AgCl(s)
16. At what temperatures are the following spontaneous? [Ex. all T, high T, etc]
a)
∆H =  and
b)
∆H =  and ∆ S = 
________________
c)
∆H = + and
____ ______________
∆S = +
__ ________________
∆S = +
17. Calculate ΔG at 25°C for the following reaction, by first calculating ΔH and ΔS. Once you've found ΔH
and ΔS, solve for ΔG using the formula:
ΔG = ΔH - T ΔS
Also - will this reaction be spontaneous at this temperature?
CH3CO2H (l) + 2 O2 (g) → 2 CO2 (g) + 2 H2O (g)
18. Calculate the standard entropy of formation of H2O(l), its standard Gibb's energy of formation, and the
equilibrium constant K for the reaction.
H2(g) + ½ O2(g) -> H2O(l)
Substance
H2(g)
O2(g)
H2O(l)
Hfo
kJ/mol
0
0
-285.83
So
J/(mol K)
130.680
205.152
69.95
19. A zinc copper battery has a voltage of 1.10 V. How much is the Gibb's energy for the redox reaction:
Zn + Cu2+ -> Zn2+ + Cu