Problem Sheet – Heat of Reaction and Chemical Equations
1. When 4.00 g of methane burns completely in oxygen, 200kJ of heat is
released. Calculate the molar enthalpy for the combustion of methane.
(ΔH = - 800 kJ)
2. When 0.726 g of carbon reacts with excess sulphur to create carbon
disulphide,
C(s) + 2 S(s) → CS2(g) , the enthalpy change is 5.40 kJ. Calculate the
molar enthalpy of formation of carbon disulphide. (ΔH = 89.3 kJ)
3. Hydrazine, N2H4(l) is used as a rocket fuel. The thermochemical equation for
the combustion of hydrazine is: N2H4 + O2 → N2 + 2 H2O ∆H = - 622 kJ.
What quantity of heat is liberated by the combustion of 1.00 g of
hydrazine? (19.5 kJ)
4. Glucose, C6H12O6(s), is converted into ethanol by yeast in the following
equation:
C6H12O6(s) → 2 C2H5OH(l) + 2 CO2(s) + 67.0 kJ.
If 47.5 g of ethanol is produced in 0.50 L of wine, how much heat is
produced? (34.6 kJ)
5. The equation of nitrogen produced in a deployed air bag is:
2 NaN3(s) + 42.7 kJ → 2 Na(s) + 3 N2(g)
What amount of heat is needed to prepare 0.325 kg of N2? (165 kJ)
6. Given the equation 2 NH3(g) + 3 N2O(g) → 4 N2(g) + 3 H2O(l) + 1010 kJ
a) What quantity of heat is liberated by the reaction of 45 g of N2O(g) with
excess ammonia? (3.4 x 102 kJ)
b) What quantity of heat is liberated by the reaction that produces of 45.0
g of N2(g)? (405 kJ)
c) What mass of ammonia is needed to produce 6.00 x 103 kJ of heat?
(202 g)
7. The amount of solar radiation received annually in Arizona is about 8.4 x 106
kJ/m2. What mass of carbon must be burned into carbon dioxide to produce
the same amount of energy in the following reaction? (2.6 x 105 g)
C(s) + O2(g) → CO2(g)
∆H = -393.5 kJ