JEE PYQ: Thermodynamics Question 14
Question 14 - 2020 (07 Jan Shift 2)
The standard heat of formation ($\Delta_f H^0_{298}$) of ethane (in kJ/mol), if the heat of combustion of ethane, hydrogen and graphite are $-1560$, $-393.5$ and $-286$ kJ/mol, respectively is ___.
Show Answer
Answer: $-192.5$
Solution
$\text{C} + \text{O}_2 \to \text{CO}_2$; $\Delta_c H^0 = -286.0$ kJ/mol …(i). $\text{H}_2 + \frac{1}{2}\text{O}_2 \to \text{H}_2\text{O}$; $\Delta_c H^0 = -393.5$ kJ/mol …(ii). $\text{C}_2\text{H}_6 + \frac{7}{2}\text{O}_2 \to 2\text{CO}_2 + 3\text{H}_2\text{O}$; $\Delta_c H^0 = -1560$ kJ/mol …(iii). $\Delta_f H^0$ of $\text{C}_2\text{H}6 = 2 \times \Delta_c^0 H[\text{C}{\text{graphite}}] + 3 \times \Delta_c H^0[\text{H}_2(g)] - \Delta_c H^0[\text{C}_2\text{H}_6(g)] = 2 \times (-286.0) + 3(-393.5) - (-1560) = -192.5$ kJ/mol.
BETA
