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: \[\ce{SO2 + 1/2O2 -> SO3}\]

Answer 1

`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