Exercise 2
: Thermodynamics
Name
: …………………
Date
: ………………
1. The diagram shows the pressure p and volume V relationship for one cycle of operation of an engine.
Determine which parts of the cycle identify isobaric, isochoric, and adiabatic changes of state.
2. The pressure and volume of a gas are changed along the path ABCA.
Using the data shown in the graph, determine the work
done in each segment of the path:
(a) A to B,
work done from A to B = ........................................ J [2]
(b) B to C
work done from B to C = ........................................ J [2]
(c) C to A.
work done from C to A = ........................................ J [2]
3. A thermodynamic system is taken from state a to c along either path abc or path adc. Along path abc
the work done W by the system is 350 J. Along path adc W is 120 J. The internal energies of the four
states shown are Ua = 200 J, Ub = 280 J, Uc = 650 J and Ud = 360 J.
Calculate the heat flow Q for each of the four processes
ab, bc,ad, and dc. In each process, does the system
absorb or liberate heat?
4. The P–V diagram shows the expansion of a fixed mass of an ideal gas, from state A to state
B. The temperature of the gas in state A is 400 K.
a. Calculate the temperature of the gas in state B.
Temperature = …………. K [2]
b. Calculate the work done by the gas in expanding
from state A to state B.
Work Done = …………. J [2]
c. Determine the amount of thermal energy transferred during the expansion from state A to
state B. If we assume the gas is isothermally expanded from state A to state B.
Thermal energy = …………. J [2]
5. A fixed mass of gas in a heat pump undergoes a cycle of changes of pressure, volume and temperature
as illustrated in the graph to the right. The gas is assumed to be ideal.
The table below shows the increase in internal energy which takes place during each of the changes A
to B, B to C and C to D. It also shows that in both of sections A to B and C to D, no heat is supplied to
the gas.
Using the first law of thermodynamics and necessary data from the graph, complete the table below.