Chem 117
graded)
Extra Practice (not
Thermodynamics Practice
The following is ungraded practice. The answer key will be posted on Canvas.
→ H2O(l)
1. Determine if the following reactions/processes increase or decrease entropy of the system.
a) 2 CO(g) + 2 NO(g) → N2(g) + 2 CO2(g)
b) 2 CH4(g) + O2(g) + CO2(g) → 3 H2(g) + 3 CO(g) + H2O(g)
c) CaCO3(s) → CaO(s) + CO2(g)
d) C(soot) → C(diamond)
2. Under what qualitative (i.e., no numbers) conditions will the following reactions/processes be
spontaneous?
a) The endothermic process of dissolving NH4NO2 in water
b) Mg(s) + Cl2(g) → MgCl2(s) ΔH = -641 kJ
c) Combustion of propane (C3H8) by C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)
3. Phase changes occur at equilibrium where ΔG = 0. Calculate the boiling point of carbon
tetrachloride given the following information.
Compound
ΔHf (kJ/mol)
S (J/mol·K)
CCl4(g)
-95.7
309.7
CCl4(l)
-128.2
216.4
4. Calculate the ΔS for the vaporization of water and ethanol (C2H5OH) at their boiling points.
Why are the ΔS for ethanol and water different than the other compounds? Note: the first four
compounds do not hydrogen bond.
Formula
bp (K)
ΔHvap (kJ/mol)
ΔSvap (J/mol·K)
C4H10O
307.8
26.5
86.1
C3H6O
329.3
29.1
88.4
C6H6
353
30.8
87.3
CHCl3
334
29.4
88.0
C2H5OH
351
38.6
H2O
373.2
40.7
0
