JEE PYQ: Thermodynamics Question 26
Question 26 - 2019 (10 Apr Shift 2)
The difference between $\Delta H$ and $\Delta U$ ($\Delta H - \Delta U$), when the combustion of one mole of heptane ($\ell$) is carried out at a temperature T, is equal to:
(1) $-4RT$
(2) $-3RT$
(3) $4RT$
(4) $3RT$
Show Answer
Answer: (1)
Solution
$\text{C}7\text{H}{16}(\ell) + 11\text{O}_2(g) \xrightarrow{\Delta} 7\text{CO}_2(g) + 8\text{H}_2\text{O}(\ell)$. $\Delta H - \Delta U = \Delta n_g RT$. $\Delta n_g =$ no. of moles of product in gaseous state $-$ no. of moles of reactant in gaseous state $= 7 - 11 = -4$. $\Delta H - \Delta U = -4RT$.
BETA
