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Question
The standard enthalpies of formation of SO2 and SO3 are −297 kJ mol−1 and −396 kJ mol−1 respectively. Calculate the standard enthalpy of reaction for the reaction: \[\ce{SO2 + 1/2O2 -> SO3}\]
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Solution
`Δ"H"_"f"^0` (SO2) = −297 kJ mol−1
`Δ"H"_"f"^0` (SO3) = −396 kJ mol−1
\[\ce{SO2 + 1/2O2 -> SO3}\]
`Δ"H"_"r"^0` = ?
`Δ"H"_"r"^0 = (Δ"H"_"f"^0)_"compound" - sum(Δ"H"_"f")_"elements"`
`Δ"H"_"r"^0 = Δ"H"_"f"^0 ("SO"_3) - [Δ"H"_"f"^0 ("SO"_2) + 1/2 Δ"H"_"f"^0 ("O"_2)]`
`Δ"H"_"r"^0` = −396 kJ mol−1 − (−297 kJ mol−1 + 0)
`Δ"H"_"r"^0` = −396 kJ mol−1 + 297
`Δ"H"_"r"^0` = − 99 kJ mol−1
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