ThermochemistryMedium

Reaction enthalpy calculation

Calculate ΔH° for: 2H₂(g) + O₂(g) → 2H₂O(l).
ΔH°_f(H₂O(l)) = -285.8 kJ/mol.

Given data

ΔH°<sub>f</sub>(H₂O(l)) = -285.8 kJ/mol

Steps

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Use ΔH°_rxn = Σ n·ΔH°_f(products) - Σ n·ΔH°_f(reactants). ΔH°_f(elements) = 0.
Write your working — the numerical result must appear in the text kJ

Full worked solution

Use ΔH°_rxn = Σ n·ΔH°_f(products) - Σ n·ΔH°_f(reactants). ΔH°_f(elements) = 0.
$2\cdot(-285.8) - 0$
$2\cdot(-285.8) - 0 = 2\times(-285.8) = -571.6 = \mathbf{-571.6\,kJ}$ . Reaction enthalpy, exothermic.

Result:ΔH° = -571.6 kJ (exothermic).

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