Thrmodynamic work

Problem 1

Find the amount of work done on the surroundings when 1 liter of an ideal gas, initially at a pressure of 10 atm, is allowed to expand at constant temperature to 10 liters by
a) reducing the external pressure to 1 atm in a single step,
b) reducing P first to 5 atm, and then to 1 atm,
c) allowing the gas to expand into an evacuated space so its total volume is 10 liters.

Solution. First, note that ΔV, which is a state function, is the same for each path:

V₂ = (10/1) × (1 L) = 10 L, so ΔV = 9 L.

For path (a), w = –(1 atm)× (9 L) = –9 L-atm.

For path (b), the work is calculated for each stage separately:

w = –(5 atm) × (2–1 L) – (1 atm) × (10–2 L) = –13 L-atm

For path (c) the process would be carried out by removing all weights from the piston in Fig. 1 so that the gas expands to 10 L against zero external pressure. In this case w = (0 atm) × 9 L = 0; that is, no work is done because there is no force to oppose the expansion.