Question

Calculate the standard enthalpy of formation (∆Hf) of water (H2O) given the following information: 2H2(g) + O2(g) → 2H2O(l); ∆H = -572 kJ/mol and the standard enthalpy of formation of O2 is 0 kJ/mol.

Answer 1

To calculate the standard enthalpy of formation of water, we need to find the enthalpy change for the formation of 1 mole of water from its elements in their standard states. The given reaction is:2H2 g  + O2 g   2H2O l ; H = -572 kJ/molFirst, we need to adjust the reaction so that it represents the formation of 1 mole of water:1/2 *  2H2 g  + O2 g   2H2O l  H2 g  + 1/2 O2 g   H2O l Now, we need to adjust the enthalpy change for this reaction. Since we have halved the reaction, we also need to halve the enthalpy change:H = -572 kJ/mol * 1/2 = -286 kJ/molSo, the standard enthalpy of formation  Hf  of water  H2O  is -286 kJ/mol.