For which one of the following equations is $\Delta \mathrm{H}_{\text {react }}^{\circ}$ equal to $\Delta…

For which one of the following equations is $\Delta \mathrm{H}_{\text {react }}^{\circ}$ equal to $\Delta \mathrm{H}_f^{\circ}$ for the product?
  1. $\mathrm{N}_{2(g)}+\mathrm{O}_{3(g)} \rightarrow \mathrm{N}_2 \mathrm{O}_3(g)$
  2. $\mathrm{CH}_{4(g)}+2 \mathrm{Cl}_{2(\mathrm{~g})} \rightarrow \mathrm{CH}_2 \mathrm{Cl}_{2(l)}+$ $2 \mathrm{HCl}_{(g)}$
  3. $\mathrm{Xe}_{(g)}+2 \mathrm{~F}_{2(g)} \rightarrow \mathrm{XeF}_{4(g)}$
  4. $2 \mathrm{CO}_{(g)}+\mathrm{O}_{2(g)} \rightarrow 2 \mathrm{CO}_{2(g)}$

Solution

Enthalpies of formation of elementary substances Xe and \(\mathrm{F}_2\) are taken as zero.
For (c) \(\Delta H_{\text {reaction }}^{\circ}\)
\(=\Delta H_f^{\circ}\left(\mathrm{XeF}_4\right)-\left[\Delta H_f^{\circ}(\mathrm{Xe})+2 \Delta H_f^{\circ}\left(\mathrm{F}_2\right)\right]\)
Thus, \(\Delta \mathrm{H}^{\circ}\) reaction \(=\Delta \mathrm{H}^{\circ}{ }_{\mathrm{f}}\left(\mathrm{XeF}_4\right)\)

Asked in: NEET 2003

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