Equations Associated with Enthalpies of Formation If the heat of formation of H2

Question

Equations Associated with Enthalpies of Formation

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?

If the heat of formation of m H_2O(l) is -286 m kJ/mol, which of the following thermochemical equations for the formation of { m H}_2{ m O} is correct?

2 H2(g) + O2(g) 2 H2O(l)       H=286 kJ H2(g) + 12 O2(g) H2O(l)       H=286 kJ 2 H(g) + O(g) H2O(l)             H=286 kJ H2O(l) H2(g) + 12 O2(g)       H=286 kJ H2(g) + O(g) H2O(g)            H=286 kJ

Explanation / Answer

H2O(l) formation:

2H2 + O2 --> 2H2O Hf = -286*2 = 572 kJ7mol

THEN:

H2 + 1/2O2 --> H2O Hf = -286

OR

H2O --> H2 + 1/2O2 Hf = 286

both are valid

from data bank (these are correct)

H2(g) + 12 O2(g) H2O(l)       H=286 kJ

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