2C(graphite) +3H2( g)→C2H6( g)ΔHf=?C2H6( g)+27O2( g)→2CO2( g)+3H2O(l)ΔH1=−1550C(graphite) +O2( g)→CO2( g)ΔH2=−393.5H2( g)+21O2( g)→H2O(/)ΔH3=−286ΔHf=2ΔH2+3ΔH3−ΔH1=95 kJ/mole2
JEE Main 2025 — Chemistry Physical Chemistry
Consider the following cases of standard enthalpy of reaction (ΔHr∘ in kJmol−1) $\begin{aligned}
& \mathrm{C}_2 \mathrm{H}_6(\mathrm{g})+\frac{7}{2} \mathrm{O}_2(\mathrm{g}) \rightarrow 2 \mathrm{CO}_2(\mathrm{g})+3 \mathrm{H}_2 \mathrm{O}(\mathrm{l}) \Delta \mathrm{H}_1^{\circ}=-1550 \
& \mathrm{C} \text { (graphite) }+\mathrm{O}_2(\mathrm{g}) \rightarrow \mathrm{CO}_2(\mathrm{g}) \quad \Delta \mathrm{H}_2^{\circ}=-393.5 \
& \mathrm{H}_2(\mathrm{g})+\frac{1}{2} \mathrm{O}_2(\mathrm{g}) \rightarrow \mathrm{H}_2 \mathrm{O}(\mathrm{l}) \quad \Delta \mathrm{H}3^{\circ}=-286
\end{aligned}Themagnitudeof\Delta \mathrm{H}{f \mathrm{C}_2 \mathrm{H}_6(\mathrm{g})}^{\circ}is _______\mathrm{kJ} \mathrm{mol}{ }^{-1}$ (Nearest integer).
Held on 22 Jan 2025 · Verified 6 Jul 2026.
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