Heat Problem Set
Name ________________________________________________
Heat Stoichiometry
1.
Consider the following reaction:
2 H2 (g) + O2 (g)  2 H2O (g)
∆H = -572 kJ
(a) How much heat is evolved for the production of 1.00 mole of H 2O?
(b) How much heat is evolved when 4.03 g H2 are reacted with excess oxygen?
(c) How much heat is evolved when 186 g oxygen are reacted with excess hydrogen?
(d) The total volume of hydrogen gas needed to fill the Hindenburg was 2.0 x 10 8 L at 1.0 atm and 25ºC. How
much heat was evolved when the Hindenburg exploded, assuming all of the hydrogen exploded?
(Zumdahl, 9th edition, Ch. 6, 46)
2.
Portable hot packs are available for skiers and people engaged in other outdoor activities in a cold climate. The
air-permeable paper packet contains a mixture of powdered iron, sodium chloride, and other components, all
moistened by a little water. The exothermic reaction that produces the heat is a very common one – the rusting of
iron:
4 Fe (s) + 3 O2 (g)  2 Fe2O3 (s)
∆H = -1644.4 kJ/mol
When the outside plastic envelope is removed, O2 molecules begin to penetrate the paper, causing the reaction to
begin. A typical packet contains 250 g of iron to warm your hands or feet for up to 4 hours. How must heat (in kJ)
is produced by this reaction?
(Chang, 11th edition, 6.104)
3.
Consider the following reaction:
2 CH3OH (g)  2 CH4 (g) + O2 (g)
∆H = + 252.8 kJ
(a) Is this reaction exothermic or endothermic?
(b) Calculate the amount of heat transferred when 24.0 g of CH 3OH (g) is decomposed by this reaction at
constant pressure.
(c) For a given sample of CH3OH, the enthalpy change during the reaction is 82.1 kJ. How many grams of
methane gas are produced?
(d) How many kilojoules of heat are released when 38.5 g of CH 4 (g) react with 14.0 g of O2 (g) at constant
pressure?
(Brown/Lemay, 12th edition, 5.44)
4.
A quantity of 2.00 x 102 mL of 0.862 M HCl is mixed with an equal volume of 0.431 M Ba(OH) 2 in a constantpressure calorimeter of negligible heat capacity. The initial temperature of the HCl and Ba(OH)2 solutions is the
same at 20.48ºC. What is the final temperature of the mixed solutions corresponding to the following equation:
H+ (aq) + OH- (aq)  H2O (l)
∆H = -56.2 kJ/mol
(Chang, 11th edition, 6.77)
5.
Meals-ready-to-eat (MREs) are military meals that can be heated on a flameless heater. The heat is produced by
the following reaction:
Mg (s) + 2 H2O (l)  Mg(OH)2 (s) + H2 (g)
∆H = -355 kJ/mol
Calculate the number of grams of Mg needed for this reaction to release enough energy to increase the
temperature of 75 mL of water from 21ºC to 79ºC.
(Brown/Lemay, 12th edition, 5.102)
Heat Problem Set
Name ________________________________________________
Heat Stoichiometry
6.
Consider the following reaction:
2 H2 (g) + O2 (g)  2 H2O (g)
∆H = -572 kJ
(e) How much heat is evolved for the production of 1.00 mole of H 2O?
(f) How much heat is evolved when 4.03 g H2 are reacted with excess oxygen?
(g) How much heat is evolved when 186 g oxygen are reacted with excess hydrogen?
(h) The total volume of hydrogen gas needed to fill the Hindenburg was 2.0 x 10 8 L at 1.0 atm and 25ºC. How
much heat was evolved when the Hindenburg exploded, assuming all of the hydrogen exploded?
(Zumdahl, 9th edition, Ch. 6, 46)
7.
Portable hot packs are available for skiers and people engaged in other outdoor activities in a cold climate. The
air-permeable paper packet contains a mixture of powdered iron, sodium chloride, and other components, all
moistened by a little water. The exothermic reaction that produces the heat is a very common one – the rusting of
iron:
4 Fe (s) + 3 O2 (g)  2 Fe2O3 (s)
∆H = -1644.4 kJ/mol
When the outside plastic envelope is removed, O2 molecules begin to penetrate the paper, causing the reaction to
begin. A typical packet contains 250 g of iron to warm your hands or feet for up to 4 hours. How must heat (in kJ)
is produced by this reaction?
(Chang, 11th edition, 6.104)
8.
Consider the following reaction:
2 CH3OH (g)  2 CH4 (g) + O2 (g)
∆H = + 252.8 kJ
(e) Is this reaction exothermic or endothermic?
(f) Calculate the amount of heat transferred when 24.0 g of CH 3OH (g) is decomposed by this reaction at
constant pressure.
(g) For a given sample of CH3OH, the enthalpy change during the reaction is 82.1 kJ. How many grams of
methane gas are produced?
(h) How many kilojoules of heat are released when 38.5 g of CH 4 (g) react with 14.0 g of O2 (g) at constant
pressure?
(Brown/Lemay, 12th edition, 5.44)
9.
A quantity of 2.00 x 102 mL of 0.862 M HCl is mixed with an equal volume of 0.431 M Ba(OH) 2 in a constantpressure calorimeter of negligible heat capacity. The initial temperature of the HCl and Ba(OH) 2 solutions is the
same at 20.48ºC. What is the final temperature of the mixed solutions corresponding to the following equation:
H+ (aq) + OH- (aq)  H2O (l)
∆H = -56.2 kJ/mol
(Chang, 11th edition, 6.77)
10. Meals-ready-to-eat (MREs) are military meals that can be heated on a flameless heater. The heat is produced by
the following reaction:
Mg (s) + 2 H2O (l)  Mg(OH)2 (s) + H2 (g)
∆H = -355 kJ/mol
Calculate the number of grams of Mg needed for this reaction to release enough energy to increase the
temperature of 75 mL of water from 21ºC to 79ºC.
(Brown/Lemay, 12th edition, 5.102)