A system absorbs 100 kJ heat in the process shown in the figure. What is Δ U for the system? — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

Heat absorbed q = +100 kJ. The work done is represented by the area under the P-V curve (a straight line from V = 1 m3 to 2 m3 and P = 1 bar to 2 bar). Area under the line (trapezium) = 0.5 * (1 + 2) bar * (2 - 1) m3 = 1.5 bar-m3 = 1.5 * 10^5 J = 150 kJ. Since it is expansion, work done BY the gas is +150 kJ => w = -150 kJ. Using Δ U = q + w = 100 - 150 = -50 kJ.