What is the change in internal energy of gas? — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

STP implies an initial temperature of $0^\circ\text{C}$. The gas is cooled to $-50^\circ\text{C}$, so $\Delta T = -50\text{ K}$. Hydrogen is a diatomic gas with $C_v = \frac{5}{2}R \approx 5\text{ cal/K-mol}$. The change in internal energy is $\Delta U = n C_v \Delta T = 4 \times 5 \times (-50) = -1000\text{ cal}$.