Question

What is the standard enthalpy of formation of hydrogen gas (H2) given that the standard enthalpy of combustion for hydrogen gas is -286 kJ/mol and the standard enthalpy of formation of water (H2O) is -285.8 kJ/mol?

Answer 1

The standard enthalpy of formation of hydrogen gas  H2  is 0 kJ/mol. This is because hydrogen gas is an element in its standard state, and the standard enthalpy of formation for any element in its standard state is defined as zero.