Question

Calculate the standard enthalpy change for the reaction 2H2(g) + O2(g) ⟶ 2H2O(g), given that the standard enthalpies of formation of H2(g), O2(g), and H2O(g) are 0 kJ/mol, 0 kJ/mol, and -242 kJ/mol, respectively.

Answer 1

To calculate the standard enthalpy change for the reaction, we can use the formula:H =  Hf products  -  Hf reactants where H is the standard enthalpy change, and Hf is the standard enthalpy of formation.For the given reaction:2H2 g  + O2 g   2H2O g H = [2  Hf H2O g  ] - [2  Hf H2 g   + Hf O2 g  ]Since the standard enthalpies of formation of H2 g  and O2 g  are 0 kJ/mol:H = [2   -242 kJ/mol ] - [2  0 kJ/mol + 0 kJ/mol]H = -484 kJ/molThe standard enthalpy change for the reaction is -484 kJ/mol.