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Thermochemistry Practice Questions

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Updated on Sep 24, 2011

Review the following concepts if needed -  Thermochemistry Study Guide

Practice Problems

1. Calculate the energy released when a 4,570 g piece of hot iron cools from 1000° C to 20° C.
2. Calculate the energy needed to heat 60 g of aluminum from 100° C to 250° C.
3. Calculate the final temperature of 295 g of water, initially at 30.0° C, if 4,500 joules are added.

 

Calculate the standard enthalpy of reaction for the following reactions (don't forget to balance the equations first!). Also, indicate whether the reaction is exothermic or endothermic.

4. C2H6(g) + O2(g) → H2O(g) + CO2(g) (combustion of ethane)
5. H2O(l) + CO2(g) → C6H12O6(s) +O2(g) (photosynthesis)
6. SO2(g) + O2(g) → SO3(g)
7. Fe(s) + O2(g) → Fe2O3(s) (oxidation of iron)

 

8.Calculate the enthalpy change for P4(s) + 6Cl2(g) → 4PCl3(l) given
P4(s) + 10Cl2(g) → 4PCl5(s) ΔH = –1774.0 kJ
PCl3(l) + Cl2(g) → PCl5(s) ΔH = –123.8 kJ
9.Calculate the enthalpy change for 2B(s) + 3H2(g)→ B2H6(g), given
4B(s) + 3O2(g) → 2B2O3(g) ΔH = –2546 kJ
B2H6(g) + 3O2(g) → 2B2O3(g) + 3H2O (g) ΔH = – 2035 kJ
H2O(l) → H2O(g) ΔH = 44kJ

 Answers

1. –2.02 * 106 J = –2020 kJ
2. 8,010 J = 8.01 kJ
3. 33.6° C
4. – 1,428 kJ, exothermic
5. 2,802 kJ, endothermic
6. –89 kJ, exothermic
7. v826 kJ, exothermic
8. –1,774.0 kJ
9. +36 kJ
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