**PRACTICE EXAM QUESTIONS:
**These are actual questions from
previous exams to help you study for the upcoming first exam.

**1) For FOUR of FIVE of
the following give a short (3-4 sentences) explanation or definition, including
equations, uses, applications, examples, etc. **

Zeroth Law of Thermodynamics; State Function; Standard Enthalpy of Formation; Maxwell Distribution; Kinetic Theory of Gases.

** **

**2) **
37.2 g of Xe is at 250 ^{o}C in a vessel
of 5.00 dm^{3}. For Xe, a = 4.250 atmL^{2}/mol^{2} and b
= 5.105 x 10^{-2} L/mol. **i) **Calculate the pressure assuming the
Xe behaves ideally. **ii) **Calculate the pressure assuming the Xe behaves as
a van der Waals gas. **iii) **Explain what (in an approximate way) the a and
b parameters in the van der Waals equation of state represent.

**
**

**3)**
For the following problem, assume combustion takes place with oxygen gas and
that carbon dioxide gas and liquid water are the only products of combustion,
and that you can look up the standard enthlpies of formation of these products.
**a) **The enthalpy of combustion of cyclopropane gas is -2091 kJ/mol. What
is the standard enthalpy of formation of cyclopropane gas? **b)** Propene gas
has a standard enthalpy of formation of +20.42 kJ/mol. What is the standard
enthalpy of combustion for propene gas? **c) W**hat is the standard enthalpy
for the isomerization reaction: cyclopropane (g) ----> propene (g)

**
**

**4)**
For the following problem, assume a vessel at 300 K containing 1.00 g each of
He, Ar, and Ne, and that all gases behave ideally. **a)** If the partial
pressure of Ar is 250 torr, what are the total pressure and volume? **b) **
Now suppose the vessel has a piston at one end and expands isothermally to twice
its final volume in a) against a constant external pressure equal to the total
pressure. What are q, w,
DU
and DH
for the expansion? **c) **Now suppose the same isothermal expansion happens
as in b) but reversibly to a final pressure equal to the total pressure. What
are q, w, DU
and DH
for the expansion?

**
5) MULTIPLE CHOICE – NO PARTIAL CREDIT**.
Circle the correct answer for each.

**i)**
Compared to the ideal gas pressure, the van der Waals pressure of a gas will:

a) Always be greater than ideal b) Always be less than ideal.

c) Always be equal to ideal d) Depend on the nature of the gas.

** **

**ii)**
In an adiabatic expansion of an ideal gas, which of the following is always
true?

a) The temperature of the gas will rise.

b) The work done by the gas on the surroundings is equal to the decrease in the internal energy of the gas.

c) No work is done by the gas on the surroundings.

d) The work done by the gas on the surroundings is equal to the increase in the internal energy of the gas.

** **

**iii)**
The standard enthalpy of fusion of silver at 1234 K is 11.30 kJ/mol. How much
energy is required to completely melt 90.0 g of silver at 1234 K?

a) +11.30 kJ b) +9.43 kJ c) +13.5 kJ d) –9.43 kJ

** **

**iv)**
DU
for the following reaction was measured at temperature T in a constant volume
calorimeter. A (s) + 2B (g)
à
2C (s) + d (g) DH^{o}
for the reaction is given approximately by

a)
DU^{o}
– RT b)
DU^{o}
c)
DU^{o}
+ RT d)
DU^{o}
+ 2RT

** **

**v)**
A vessel of volume 22.4 L contains 3.0 mol O_{2} and 4.5 mol N_{2}
at 273.15 K. The partial pressures in atmospheres of O_{2} and N_{2
}respectively, are

a) 0.4 and 0.6 b) 7.5 and 7.5 c) 3.0 and 4.5 d) 4.5 and 3.0

Answers:

1) See text book

2) i) P = 2.43 atm ii) 2.43 atm (OK, 2.4253 atm) iii) a is intermolecular force correction (as real gas molecules do interact with each other) and b is a volume correction (as real gas molecules are not negligibly small).

3) Can look up the standard enthalpy of formation for CO2 and H2O.

a) +53 kJ/mol b) -2058 kJ/mol c) -33 kJ/mol

4) a) P = 4.26 atm, V = 1.87 L

b) w = -809 J, q = +809 J, Delta U = Delta q = 0 J

c) w = -561 J, q = +561 J, Delta U = Delta q = 0 J

5 i) answer is d (subtracting a makes pressure smaller, dividing by decreased volume (less nb) makes pressure larger, so it depends on the a and b terms and hence the gas)

5 ii) answer is b (adiabatic so q is zero, Delta U is work, and decreases as work done by system in expansion)

5 iii) answer is b) (moles times enthalpy give 9.43 kJ, positive as must add energy to system (silver) to melt it)

5 iv) answer is a) (H = U + PV, so Delta H = Delta U + Delta n(gas)RT and Delta n(gas) is -1)

5 v) answer is c (lots of ways to calculate this from ideal gas law)