Question

What is the enthalpy change in kilojoules for the reaction:2H2(g) + O2(g) → 2H2O(l)given that the standard enthalpy of formation for liquid water is -285.8 kJ/mol, and the standard enthalpy of formation for hydrogen gas and oxygen gas are 0 kJ/mol?

Answer 1

To calculate the enthalpy change for the reaction, we can use the following formula:H = nHf products  - nHf reactants where H is the enthalpy change for the reaction, n is the stoichiometric coefficient, and Hf is the standard enthalpy of formation.For the given reaction:2H2 g  + O2 g   2H2O l The standard enthalpy of formation for the reactants are:Hf H2  = 0 kJ/molHf O2  = 0 kJ/molThe standard enthalpy of formation for the product is:Hf H2O  = -285.8 kJ/molNow, we can plug these values into the formula:H = [2   -285.8 ] - [2  0 + 1  0]H =  -571.6  - 0H = -571.6 kJThe enthalpy change for the reaction is -571.6 kJ.