Consider the following cases of standard enthalpy of reaction ​(ΔH°r in kJmol^-1)

Question

Consider the following cases of standard enthalpy of reaction \(\left(\Delta \mathrm{H}_{\mathrm{r}}^{\mathrm{o}}\right.\ in \ \left.\mathrm{kJ} \mathrm{mol}^{-1}\right)\)

\( \mathrm{C}_{2} \mathrm{H}_{6}(\mathrm{~g})+\frac{7}{2} \mathrm{O}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{CO}_{2}(\mathrm{~g})+3 \mathrm{H}_{2} \mathrm{O}(\ell) \Delta \mathrm{H}_{1}^{\mathrm{o}}=-1550\)

\( C (graphite) +\mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{CO}_{2}(\mathrm{~g}) \Delta \mathrm{H}_{2}^{\mathrm{o}}=-393.5\)

\( \mathrm{H}_{2}(\mathrm{~g})+\frac{1}{2} \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{H}_{2} \mathrm{O}(\ell) \Delta \mathrm{H}_{3}^{\mathrm{o}}=-286\)  

The magnitude of \(\Delta H^o_{f C_2H_6(g)}\) is ......... kJ \(mol^{-1}\)(Nearest integer).

Answer 1

Answer is: 95

\(2 \mathrm{C}_{\text {(graphite) }}+3 \mathrm{H}_{2}(\mathrm{~g}) \rightarrow \mathrm{C}_{2} \mathrm{H}_{6}(\mathrm{~g}) \quad \Delta \mathrm{H}_{\mathrm{f}}= ?\)

\(C_2H_6 (g) + \frac{7}{2} O_2(g) \rightarrow 2CO_2(g) + 3H_2O(l) \ \Delta H_1 = -1550\)

\(C_{\text{graphite}} + O_2(g) \rightarrow CO_2(g) \ \Delta H_2=-393.5\)

\(H_2(g) + \frac{1}{2} O_2(g) \rightarrow H_2O(l) \ \Delta H_3 = -286\)

\(\Delta H_f = 2\Delta H_2 + 3\Delta H_3 - \Delta H_1 \)

\(=95 \ kJ/ \text{mole}\)