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