CHEM 202
HOMEWORK 1
Chapter one
1. Consider the following reactions:
(a) Hg (l )  Hg ( g )
(b) 3O2 ( g )  2O3 ( g )
(c) CuSO4 .5 H 2 O( s)  CuSO 4 ( s)  5H 2 O ( g )
(d) H 2 ( g )  F2 ( g )  2 HF ( g )
At constant pressure, in which of the reactions is work done by the
system on the surrounding? By the surrounding on the system? In
which of them no work is done?
2. A gas expands in volume from 20mL to 50 mL at constant
temperature. Calculate the work done (in joules) if the gas expands (a)
against a vacuum, (b) against a constant pressure of 3 atm?
3. Consider the reaction
H 2 ( g )  Cl 2 ( g )  2 HCl ( g )
H  -184.6kJ/mol
If 5 moles of H2 react with 5 moles of Cl2 to form HCl, calculate the
work done (in joules) against a pressure of 1 atm at 30 °C. What is ΔE
for this reaction? Assume the reaction goes to completion.
4. A piece of silver of mass 362 g has a heat capacity of 85.7 J/°C. What
is the specific heat of silver?
5. The standard enthalpy change for the following reaction is 436.4
kJ/mol:
H 2 (g)  H (g)  H (g)
Calculate the standard enthalpy of formation of atomic hydrogen(H)?
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CHEM 202
HOMEWORK 1
6. From the following heats of combustion,
3
O 2 ( g )  CO2 ( g )  2 H 2 O (l )
2
C ( graphite)  O2 ( g )  CO 2 ( g )
1
H 2 ( g )  O2 ( g )  H 2 O (l )
2
CH 3OH (l ) 
H rxn  726.4kJ / mol
H rxn  393.5kJ / mol
H rxn  285.8kJ / mol
Calculate the enthalpy of formation of methanol (CH3OH) from its
elements:
1
C ( garaphite)  2 H 2 ( g )  O2 ( g )  CH 3 OH (l )
2
7. Hydrazine, N2H4, decompose according to the following reaction:
3 N 2 H 4 (l )  4 NH 3 ( g )  N 2 ( g )
Given that the standard enthalpy of formation of hydrazine is 50.42
kJ/mol and for NH3 is -46.3 kJ/mol, calculate ΔH° for hydrazine
decomposition?
8. A 6.22 Kg piece of copper metal is heated from 30.5 °C to 350 °C.
Calculate the heat absorbed (in kJ) by the metal? (specific heat of
copper is 0.385 J/g.°C).
9. Determine the amount of heat (in kJ) given off when 1.26x104 g of
NO2 are produced according to the equation
2 NO ( g )  O2 ( g )  2 NO2 ( g )
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H  -114.6kJ/mol