What is the change in internal energy when a gas contracts from 325 ml to 125 ml at a constant press — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

By the First Law, $\Delta U = q + W$. Heat removed $q = -124 \text{ J}$. Work done on the gas during contraction $W = -P \Delta V = -2 \text{ bar} \times (125 - 325) \times 10^{-3} \text{ L} = -2 \times (-0.2) \text{ bar L} = 0.4 \text{ bar L}$. Converting to Joules ($1 \text{ bar L} = 100 \text{ J}$), $W = 40 \text{ J}$. $\Delta U = -124 \text{ J} + 40 \text{ J} = -84 \text{ J}$.