Given, ${\rm{C}} + {{\rm{O}}_2} \to {\rm{C}}{{\rm{O}}_2} + 94.2{\rm{kcal}} \ldots {\rm{.}}\left( {\rm{i}} \right)$${{\rm{H}}_2} + \frac{1}{2}{{\rm{O}}_2} \to {{\rm{H}}_2}{\rm{O}} + 68.3{\rm{kcal}} \ldots .\left( {{\rm{ii}}} \right)$${\rm{C}}{{\rm{H}}_4} + 2{{\rm{O}}_2} \to {\rm{C}}{{\rm{O}}_2} + 2{{\rm{H}}_2}{\rm{O}} + 210.8{\rm{kcal}} \ldots {\rm{.}}\left( {{\rm{iii}}} \right)$The heat of formation in kcal will be :

NEET UG CHEMISTRY MCQ: THERMODYNAMICS

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Application +4 | -1

Given,

\mathrm{C} + {\mathrm{O}_2} \to \mathrm{C}{\mathrm{O}_2} + 94.2\mathrm{kcal} \ldots \mathrm{.}\left( \mathrm{i} \right)

{\mathrm{H}_2} + \frac{1}{2}{\mathrm{O}_2} \to {\mathrm{H}_2}\mathrm{O} + 68.3\mathrm{kcal} \ldots .\left( {\mathrm{ii}} \right)

\mathrm{C}{\mathrm{H}_4} + 2{\mathrm{O}_2} \to \mathrm{C}{\mathrm{O}_2} + 2{\mathrm{H}_2}\mathrm{O} + 210.8\mathrm{kcal} \ldots \mathrm{.}\left( {\mathrm{iii}} \right)

The heat of formation in kcal will be :

View answer and explanation

Correct option: C

-20

Option C (-20) is correct because it correctly calculates the heat of formation of methane by using Hess's Law and the given combustion reactions.