First Law of Thermodynamics
Name
Date
Use the following P-V diagram to answer questions about this thermodynamic cycle consisting of three processes labeled ab, bc, and ca.
Pa = 3.00 × 10^5Pa, Pb = 1.00 × 10^5Pa, Va = 3 × 10^-3m^3, Vc = 9 × 10^-3m^3.
a) Identify the type of thermodynamic processes for each part of the cycle (ab, bc, ca) as:
ab:
i) adiabatic
ii) isobaric
iii) isochoric
iv) isothermal
v) none of these
bc:
i) adiabatic
ii) isobaric
iii) isochoric
iv) isothermal
v) none of these
ca:
i) adiabatic
ii) isobaric
iii) isochoric
iv) isothermal
v) none of these
b) For the process ab, determine (i) the work Wab done by the gas and (ii) the change in internal energy of the system for a heat loss of 900 J. [Hints: for (i) recall that W is the area under the curve; for (ii) use the 1st Law.]
c) For the process bc, determine (i) the work Wbc done by the gas and (ii) the change in internal energy of the system for a heat gain of 1250 J.
d) For the process ca, determine (i) the work Wca done by the gas and (ii) the change in internal energy of the system for a heat gain of 150 J.
e) Determine the total work Wtot done by the gas in the cycle. Compare this to the area of the triangle. Note that both are negative. Also note that the total change in internal energy is zero, as it must be when the system returns to the same state.