Ch 9 Thermo

Welcome to Chem 1B CLAS
with Eric Engel
Webpage: clas.sa.ucsb.edu/staff/eric
Email: eric.engel@sa.ucsb.edu
Drop-In Hours: M 10-11, 4-5
Tu 3-5
W 10-11, 4-5
in SRB 3274
Th 4-5
F 12-1
Thermodynamics (Ch 9)
1. Fill in the following table:
Positive (+)
Heat (q)
Work (w)
ΔE
Negative (-)
Zero (0)
Thermodynamics (Ch 9)
Constant Pressure
q
w
ΔE
ΔH
qp = nCp ΔT
qp = ΔH
Constant Volume
qv = nCv ΔT
qv = ΔE
w = -Pext ΔV
w=0
or –nR ΔT or - ΔngRT
ΔE = q + w
ΔE = nCv ΔT
ΔH = ΔE + Δ(PV)
ΔH = nCp ΔT
Thermodynamics (Ch 9)
2. Calculate the value of q, w, ΔE and ΔH for the following:
a. 3 moles of a monatomic ideal gas is heated from 35 to 45 °C at a
constant pressure of 3.6 atm.
b. heating 500. g of nitrogen gas from 50.0 ˚C to 75.0 ˚C in a rigid
container (for N2, Cv = 20.71 J/K mol and Cp = 29.03 J/K mol)
c. cooling 500 g of nitrogen gas from 75.0 ˚C to 50.0 ˚C at a
constant pressure of 1.00 atm
d. The pressure of a 4.2 mole sample of N2 gas is decreased from
8.7 atm to 2.5 atm at a constant volume of 20.0 L.
Thermodynamics (Ch 9)
3. Consider 2.00 mol of a monatomic ideal gas
that is taken from state A (2.0 atm, 10.0 L) to
state B (1.00 atm, 30.0 L) by two different
pathways:
Path 1: A (2.0 atm, 10. L)  C (2.0 atm, 30. L) 
B (1.0 atm, 30. L)
Path 2: A (2.0 atm, 10. L)  D (1.0 atm, 10. L) 
B (1.0 atm, 30. L)
Calculate q, w, ΔE and ΔH for both pathways.
Thermodynamics (Ch 9)
4. Concept questions:
a. For every gas, why is the value of Cp greater
than Cv? By what constant are they related?
b. Why is the value of Cp greater for nitrogen
gas than neon?
Thermodynamics (Ch 9)
5. Predict the sign of q,w, Δ E and Δ H for the following
that take place at 25 °C and 1 atm:
a. 2 H (g)  H2 (g)
b. N2(g) + 3H2(g)  2NH3(g)
(only predict w)
c. Fe2O3(s) + 3H2(g)  2Fe(s) + 3H2O(l) (only predict w)
d. H2O(l)  H2O(s)
e. Ammonium chloride is dissolved in water, and the
solution’s temperature decreases.
Thermodynamics (Ch 9)
6. Calculate the heat released or absorbed for:
a. 12 g of ammonia reacts with 25 g of oxygen
according to the following reaction:
4NH3 + 5O2  4NO + 6H2O ΔH = -338 kJ
b. Melting 36.0 g of ice at 0 °C and raising the
temperature to 50.0 ° C.
(ΔHfusion = 6.02 kJ/mol, CH2O liquid = 4.18 J/gC)
Thermodynamics (Ch 9)
7. If a 50.0 g sample of copper is heated to
85.0 ˚C and placed in 100 mL of water
initially at 25.0 ˚C, what will be the final
temperature of the water assuming no heat is
lost to the surroundings?
(Cwater = 4.18 J/g ˚C, Ccu = 0.20 J/g ˚C)
Thermodynamics (Ch 9)
8. Consider the dissolution reaction:
CaCl2(s)  Ca2+(aq) + 2Cl-(aq) ΔH = -81.5 kJ
If 20.0 g of calcium chloride are dissolved in
150. mL of water at 25.0 ˚C, what will be the
final temperature of the solution assuming no
heat loss to surroundings?
(assume heat capacity of solution is 4.18 J/g C)
Thermodynamics (Ch 9)
9. Given the following:
P4(s) + 6Cl2(g)  4PCl3(g)
P4(s) + 5O2(g)  P4O10(s)
PCl3(g) + Cl2(g)  PCl5(g)
PCl3(g) + ½ O2(g)  Cl3PO(g)
Calculate ΔH for the reaction:
P4O10(s) + 6 PCl5(g)  10 Cl3PO(g)
ΔH = -1226 kJ
ΔH = -2967 kJ
ΔH = -84 kJ
ΔH = -286 kJ
Thermodynamics (Ch 9)
10. Write the reaction that corresponds to the
enthalpy of formation of the following
compounds:
a. CH4 (g)
b. NaCl (s)
c. CH3OH (l)
Thermodynamics (Ch 9)
11. How much heat is released when 1 mole of
methane (CH4) is burned? Use the following
data:
ΔHf˚
CH4 (g)
-75 kJ/mol
CO2 (g)
-394 kJ/mol
H2O(g)
-242 kJ/mol
Thermodynamics (Ch 9)
Bonus Q:
If the heat of vaporization of water is
41 kJ/mol, what is the heat of formation of
liquid water? (hint: use data from the last
problem)
Thermodynamics (Ch 9)