Enthalpy of formation of... |JEE Main 2024

JEE MAINS 2024

09.04.24 S1

Question

The enthalpy of formation of ethane (C_2 H_6 ) from ethylene by addition of hydrogen where the bondenergies of C-H,C-C,H-H are 414 kJ,347 kJ, 615 kJ and 435 kJ respectively is kJ.

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Solution

$\begin{aligned} & \mathrm{C}_2 \mathrm{H}_4(\mathrm{~g})+\mathrm{H}_2(\mathrm{~g}) \rightarrow \mathrm{C}_2 \mathrm{H}_6(\mathrm{~g}) \\ & \Delta \mathrm{H}=\mathrm{BE}(\mathrm{C}=\mathrm{C})+4 \mathrm{BE}(\mathrm{C}-\mathrm{H})+\mathrm{BE}(\mathrm{H}-\mathrm{H})-\mathrm{BE}(\mathrm{C}-\mathrm{C})-6 \mathrm{BE}(\mathrm{C}-\mathrm{H}) \\ & \Delta \mathrm{H}=\mathrm{BE}(\mathrm{C}=\mathrm{C})+\mathrm{BE}(\mathrm{H}-\mathrm{H})-\mathrm{BE}(\mathrm{C}-\mathrm{C}) \\ & -2 \mathrm{BE}(\mathrm{C}-\mathrm{H}) \\ & =615+435-347-2 \times 414 \\ & =-125 \mathrm{~kJ}\end{aligned}$

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JEE Main

Chemistry

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