Problem: If the heat of formation of H2O(l) is -286 kJ/mol, which of the following thermochemical equations for the formation of H2O is correct?  a) H2 (g) + 1 /2 O2 (g) → H2O(l)   ΔH = − 286 kJ b) 2 H(g) + O(g) → H2O(l)            ΔH = − 286 kJ c) H2 (g) + O(g) → H2O(g)           ΔH = − 286 kJ d) H2O(l) → H2 (g) + 1/2 O2 (g)    ΔH = 286 kJ e) 2 H2 (g) + O2 (g) → 2 H2O(l)   ΔH = − 286 kJ

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The standard enthalpy of formation (ΔH˚f) refers to the enthalpy change for the formation of 1 mole of a compound from its elements in their standard states.

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Problem Details

If the heat of formation of H2O(l) is -286 kJ/mol, which of the following thermochemical equations for the formation of H2O is correct?  


a) H2 (g) + 1 /2 O2 (g) → H2O(l)   ΔH = − 286 kJ 

b) 2 H(g) + O(g) → H2O(l)            ΔH = − 286 kJ 

c) H2 (g) + O(g) → H2O(g)           ΔH = − 286 kJ 

d) H2O(l) → H2 (g) + 1/2 O2 (g)    ΔH = 286 kJ 

e) 2 H2 (g) + O2 (g) → 2 H2O(l)   ΔH = − 286 kJ

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