Water can be produced in many ways. The heat requirement for the production of water is called the HEAT OF FORMATION. In the heat of formation of water, hydrogen gas and oxygen as is needed in the reaction.
H2(g) + 1/2O2(g) -> H2O (l) ∆H= -286 KJ mol-1
H2(g) + 1/2O2(g) -> H2O (g) ∆H= -244 KJ mol-1
**water can be formd as gas or liquid
There are ways in getting the heat required for the formation of water.
1. When 1 mole of water is formed, 1mole of H-H bonds breaks and 1/2 mole of O-O is broken.
dH = nHof products - nH of reactants
dH = 2(O-H) - [(H-H) + (1/2 O-O)]
values of H-H, O-O and O-H are given.
2. Formation of water may be considered as combustion of H2, so
dH = standard enthalpy of combustion of H2