General Chemistry II: Thermochemistry Problems
1. How much heat is required to raise 5.45 g of copper from 25.0 oC to 37.5 oC? Please express your answer in joules (J),
Calories (Cal), and also kilowatt-hours (kWh).
2. If a 150.0 g block of iron (Fe) at 65 oC is added to 500.0 mL of water at 25 oC, what is the final temperature of the
mixture? Assume a density of 1.00 g/mL for water. Report to the nearest degree.
3. Nail polish is primarily made of a compound called acetone. If 100.0 mL of acetone is burned, how much
heat is released? H for the combustion reaction is -1790 kJ/mol. The density of acetone is 0.788 g/mL.
Please include the balanced chemical equation for the combustion.
4. Calculate the enthalpy change (H) for this reaction:
NO (g) + O (g)  NO2 (g)
H = ?
Using only the following information:
2 O3 (g)  3 O2 (g)
H = -427 kJ/mol
O2 (g)  2 O (g)
H = +495 kJ/mol
NO (g) + O3 (g)  NO2 (g) + O2 (g)
H = -199 kJ/mol
General Chemistry II: Thermochemistry Problems
1. How much heat is required to raise 5.45 g of copper from 25.0 oC to 37.5 oC? Please express your answer in joules (J),
Calories (Cal), and also kilowatt-hours (kWh).
q  mass  C  T

  12.5 oC   26.2J
o  

g C

3
 1cal   Cal 
26.2 J  
  6.27  10 Cal

 J   1000cal 

5.45 g   0.385
J
6
 W sec   kW   hr 
26.2 J  
  7.28  10 kWh


sec
3600
W
1000
J

 
 

2. If a 150.0 g block of iron (Fe) at 65 oC is added to 500.0 mL of water at 25 oC, what is the final temperature of the
mixture? Assume a density of 1.00 g/mL for water. Report to the nearest degree.
qcold  qhot
5004.18T  25  1500.449T  65
2090(T  25)  67.35(T  65)
2090T  52250  67.35T  4377.75
2157.35T  56627.75
56627.75
o
T
 26 C
2157.35
3. Nail polish is primarily made of a compound called acetone. If 100.0 mL of acetone is burned, how much
heat is released? H for the combustion reaction is -1790 kJ/mol. The density of acetone is 0.788 g/mL.
Please include the balanced chemical equation for the combustion.
C3 H 6O(l )  4O2( g )  3CO2( g )  3H 2O( g )
3  12.011
6  1.00794
100mL 
1 15.9994
0.788 g
mol 1790kJ


 2430kJ
mL
58.08 g
mol
 58.08
4. Calculate the enthalpy change (H) for this reaction:
NO (g) + O (g)  NO2 (g)
H = ?
Using only the following information:
2 O3 (g)  3 O2 (g)
H = -427 kJ/mol
O2 (g)  2 O (g)
H = +495 kJ/mol
NO (g) + O3 (g)  NO2 (g) + O2 (g)
H = -199 kJ/mol
NO( g )  O3( g )  NO2( g )  O2( g )

1
3O2( g )  2O3( g )
2

1
2O( g )  O2( g )
2


  199
1
   (427)
2
1
   (495)
2
ΔΗ  233 kJ/mol
Comprehensive Problem
How much total heat is needed to completely vaporize 260 grams of ice at -15 oC to steam at 125 oC? Assume the
approximate 1.0 gram per mL density throughout.
Data Needed:
Cp (ice) =
2.11
Cp (water) =
4.18
Cp (steam) =
2.08
J
g oC
J
g oC
J
g oC
Hfus (water) =
Hvap (water) =
kJ
mol
kJ
40.7
mol
6.02
Solution
Heat the ice:
260 g 
2.11J
Melt the ice:
260 g 
mol 6.02kJ

 86.9kJ
18.01g
mol
Heat the water:
260 g 
4.18 J
Boil the water:
260 g 
mol
40.7kJ

 587.56kJ
18.01g
mol
Heat the steam:
260 g 
2.08 J
g oC
g oC
g oC
15oC  8229 J  8.2kJ
100oC  108680 J  108.7kJ
 25oC  13520 J  13.5kJ
Total heat required:
8.2
86.9
108.7
587.6
13.5
______
804.9 kJ = 8.0 x 102 kJ