JEE PYQ: Thermodynamics Question 6
Question 6 - 2020 (02 Sep Shift 1)
The internal energy change (in J) when 90 g of water undergoes complete evaporation at $100^\circ$C is ___.
(Given: $\Delta H_{\text{vap}}$ for water at 373 K $= 41$ kJ/mol, $R = 8.314$ JK$^{-1}$ mol$^{-1}$)
Show Answer
Answer: 189494
Solution
$\Delta H = \Delta U + \Delta n_g RT$. $n = \frac{90}{18} = 5$ mol. $\text{H}_2\text{O}(\ell) \rightleftharpoons \text{H}_2\text{O}(g)$, $\Delta n = 1$. $41000 = \Delta U + 1 \times 8.314 \times 373$. $\Delta U = 37898.875$ J. For 5 moles, $\Delta U = 37898.87 \times 5 = 189494$ J.
BETA
