Question

Write the expression for the work done by 1 mole of the gas in each of the following cases: 

(i) For irreversible expansion of the gas from V₁ toV₂ 

(ii) For reversible isothermal expansion of the gas from V₁ toV₂.

Answer 1

(i) Irreversible expansion takes place when external pressure is constant 

W_irr = – P_ext(V₂ – V₁) = – P_extΔV 

(ii) Reversible expansion takes place when internal pressure is infinitesimally greater than external pressure at every stage W_rev = -nRTln(V₂/V₁)