Question

What is the work done by 0.5 m^3 saturated ethanol which evaporates to 20 kPa atmosphere to form 2 m^3 of water vapor?

(a) 20 kJ

(b) -20 kJ

(c) 30 kJ

(d) -30 kJ

This question was posed to me in an international level competition.

The doubt is from Ideal Reversible Processes topic in section Energy Balances that Include the Effects of Chemical Reaction, Ideal Processes, Efficiency and the Mechanical Energy Balance and Heats of Solution and Mixing of Basic Chemical Engineering

Answer 1

Right option is (d) -30 kJ

Easy explanation: Work done = -p∆V = -20*(2 – 0.5) = -30 kJ.