When an electric current of 0.50 A from a 12 V supply is passed for through a resistance in thermal — Thermodynamics and Thermochemistry Chemistry Question
Question
When an electric current of 0.50 A from a 12 V supply is passed for $\frac{1805}{6}\text{ sec}$ through a resistance in thermal contact with water maintained at 1 atm and 373 K, it is found that 0.9 g of water is vaporized. The molar internal energy change (in kJ/mol) of water is (Take $8.314 \times 373 = 3100$)
Answer: 0033
💡 Solution & Explanation
Heat supplied $q = VIt = 12 \times 0.50 \times (1805/6) = 1805\text{ J}$. Moles of water $n = 0.9/18 = 0.05\text{ mol}$. Molar heat of vaporization $\Delta H_m = 1805 / 0.05 = 36100\text{ J/mol} = 36.1\text{ kJ/mol}$. For $\text{H}_2\text{O(l)} \to \text{H}_2\text{O(g)}$, $\Delta n_g = 1$. $\Delta U_m = \Delta H_m - RT = 36100 - 3100 = 33000\text{ J/mol} = 33\text{ kJ/mol}$. Format as 0033.
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