Total change in (in kJ) going from State 1 to State 3 is — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

Stage 1 to 2: $\Delta U = 0$. Stage 2 to 3 involves heating liquid and vaporizing a portion. Heating 0.9 kg liquid from 353 K to 373 K: $\Delta U_1 = 900\text{ g} \times 4.2\text{ J/gK} \times 20\text{ K} = 75600\text{ J} = 75.6\text{ kJ}$. Vaporizing 0.45 kg (25 moles) at 373 K: $\Delta U_2 = \Delta H_{\text{vap}} - \Delta n_g RT = (25 \times 40\text{ kJ}) - (25 \times 8 \times 373 / 1000) = 1000 - 74.6 = 925.4\text{ kJ}$. Total $\Delta U = 75.6 + 925.4 = 1001\text{ kJ}$.