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For the reaction H2(g) + 1/2 O2(g) → H2O(l), where the enthalpy of formation (ΔHf) is given as −285.9 kJ mol⁻¹, determine the value of ΔHf.

1. −285.9 kJ mol⁻¹
2. −241.8 kJ mol⁻¹
3. −44.1 kJ mol⁻¹
4. Not listed among these options

Correct answer: −285.9 kJ mol⁻¹

Solution

The enthalpy of formation of liquid water is given directly in the problem as -285.9 kJ/mol, which is the value asked for. The correct option is therefore -285.9 kJ/mol.

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