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Question
Answer in brief.
What is the standard enthalpy of combustion? Give an example.
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Solution
- The standard enthalpy of combustion of a substance is the standard enthalpy change accompanying a reaction in which one mole of the substance in its standard state is completely oxidised.
- Consider the reaction,
C2H2(g) + `5/2` O2(g) → 2CO2(g) + H2O(l), Δr H° = - 1300 kJ
In the above reaction, the standard enthalpy change of the oxidation reaction, –1300 kJ is the standard enthalpy of combustion of C2H2(g).
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\[\begin{array}{cc}
\phantom{}\ce{H}\phantom{...}\ce{H}\phantom{...................}\ce{H}\phantom{...}\ce{H}\phantom{....}\\
\phantom{.}|\phantom{....}|\phantom{....................}|\phantom{....}|\phantom{.....}\\
\ce{C = C + H - H -> H - C - C - H}\\
\phantom{.}|\phantom{....}|\phantom{....................}|\phantom{....}|\phantom{.....}\\
\phantom{}\ce{H}\phantom{...}\ce{H}\phantom{...................}\ce{H}\phantom{...}\ce{H}\phantom{....}
\end{array}\]
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