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Question: Answered & Verified by Expert
IfC(s) $+\mathrm{O}_2(\mathrm{~g}) \longrightarrow \mathrm{CO}_2(\mathrm{~g}) ; \Delta \mathrm{H}=\mathrm{R}$ and $\mathrm{CO}(\mathrm{g})+\frac{1}{2} \mathrm{O}_2(\mathrm{~g}) \longrightarrow \mathrm{CO}_2(\mathrm{~g}) ; \Delta \mathrm{H}=\mathrm{S}$, then heat of formation of $\mathrm{CO}$ is:
ChemistryThermodynamics (C)VITEEEVITEEE 2021
Options:
  • A $\mathrm{R}+\mathrm{S}$
  • B $\mathrm{R}-\mathrm{S}$
  • C $\mathrm{R} \times \mathrm{S}$
  • D $\mathrm{S}-\mathrm{R}$
Solution:
1161 Upvotes Verified Answer
The correct answer is: $\mathrm{R}-\mathrm{S}$
Let, $\mathrm{C}(\mathrm{s})+\mathrm{O}_2(\mathrm{~g}) \longrightarrow \mathrm{CO}_2(\mathrm{~g}) ; \Delta \mathrm{H}=\mathrm{R}$ and $\mathrm{CO}(\mathrm{g})+\frac{1}{2} \mathrm{O}_2(\mathrm{~g}) \longrightarrow \mathrm{CO}_2(\mathrm{~g}) ; \Delta \mathrm{H}=\mathrm{S}$ (ii) Subtrācting ęu. (i) from èu (ii), wê get $\mathrm{C}(\mathrm{s})+\frac{1}{2} \mathrm{O}_2(\mathrm{~g}) \longrightarrow \mathrm{CO}(\mathrm{g}) ; \Delta \mathrm{H}=\mathrm{R}-\mathrm{S}$ Hence, heat of formation of $\mathrm{CO}=\mathrm{R}-\mathrm{S}$

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