A system absorbs 20 kJ heat and does 10 kJ of work. The internal energy of the system — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

By the First Law of Thermodynamics, $\Delta U = q + w$. The system absorbs heat ($q = +20\text{ kJ}$) and does work on the surroundings ($w = -10\text{ kJ}$). $\Delta U = 20 - 10 = +10\text{ kJ}$. Thus, it increases by 10 kJ.