PAC 224
TEST 1
10 September 2018
1. The pressure of a confined gas is increased from P1 to P2 and the variation of the volume with
changing temperature is recorded. On the same set of axes, show the expected trend in this
variation.
(5)
2. Mercury in a barometer can be replaced by any liquid. Suppose two liquids X and Y are used in
separate barometers and the cross-sectional areas of the two capillary are the same A. Derive an
expression that relates the heights of the liquid columns in the two barometers.
(5)
3. A gas at a total pressure of 107 kPa and a volume of 500 cm3 over water at 35 °C, is compressed
to a volume of 250 cm3, also over water at 35 °C. Calculate the final pressure of the wet gas.
(5)
4. A fixed quantity of an ideal gas is compressed isothermally by a constant external pressure, Pext,
such that the gas pressure changes from P1 to P2 and its volume changes from V1 to V2.
(a) Show graphically the work done in the compression by shading the area in the graph that
indicates the work done.
(5)
(b) Derive a mathematical expression for the work done in terms of the relevant given variables. (3)
5(a) What was the conclusion of the Joule-Thomson? (b) Why was this conclusion not correct?
(c) Why is this conclusion true for ideal gases only?
(6)
6. Solid carbon in the form of graphite burns in oxygen gas to produce carbon dioxide at a pressure
of 750 mmHg. Suppose 3.0 g of carbon reacts with enough oxygen in a calorimeter such that the
temperature of the calorimeter increases from 20 °C to 30 °C. The calorimeter consumes 23 kJ for
its temperature to increase by one degree Celsius. Calculate the heat released when 9.0 g of carbon
are used instead of the 3.0 g.
(5)
7. Using data tables, calculate the heat released for the combustion of 1 mole of graphite at 25 °C.
(6)
Additional information: R = 8.314 J.mol-1.K-1 = 8.314 kPa.dm3.mol-1.K-1
= 0.082 atm.L.mol-1.K-1
The vapour pressure of water at 25 °C and 35 °C is 3.17 kPa and 5.63 kPa respectively.
Species
C2 (g)
C (g)
CO (g)
O (g)
O2 (g)
CO2 (g)
CO2 (aq)
CO32- (aq)
C (diamond)
C (graphite)
O3 (g)
ΔfH° (kJ/mol)
+ 831.90
+ 716.68
- 110.53
+ 249.17
0
- 393.51
- 413.80
- 677.14
+ 1.895
0
+ 142.7