Question
Does the following reaction represent a thermochemical equation?
$CH _{4( g )}+2 O _{2( g )} \longrightarrow CO _{2( g )}+2 H _2 O _{( g )}$
, $\Delta_{ f } H ^{\circ}=-900 kJ mol ^{-1}$

Answer

No, the given reaction does not represent a thermochemical equation. The given standard enthalpy of reaction $(\triangle _rH^\circ )$ indicates the enthalpy change accompanying the reaction when the reactants and products involved are in their standard states. The standard state of water is $H_2O_{(l)}$​​​​​​​ and not $H_2O_{(g)}$​​​​​​​​​​​​​​.

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