JEE PYQ: Thermodynamics Question 7
Question 7 - 2020 (02 Sep Shift 2)
The heat of combustion of ethanol into carbon dioxide and water is $-327$ kcal at constant pressure. The heat evolved (in cal) at constant volume and $27^\circ$C (if all gases behave ideally) is ($R = 2$ cal mol$^{-1}$ K$^{-1}$) ___.
Show Answer
Answer: $-326400$
Solution
$\text{C}_2\text{H}_5\text{OH}(\ell) + \text{O}_2(g) \to 2\text{CO}_2(g) + 3\text{H}_2\text{O}(\ell)$. $\Delta H_c = -327$ kcal. $\Delta H = \Delta U + \Delta n_g RT$. $-327 \times 10^3 = \Delta U + (-1) \times 2 \times 300$. $\Delta U = -327 \times 10^3 + 600 = -326400$ cal.
BETA
