Question

What is the standard enthalpy change for the reaction 2H₂(g) + O₂(g) -> 2H₂O(l), given the standard enthalpies of formation for H₂O(l), H₂(g) and O₂(g) as -285.8 kJ/mol, 0 kJ/mol and 0 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 for the reaction, and Hf is the standard enthalpy of formation for each substance.For the given reaction:2H g  + O g  -> 2HO l The standard enthalpies of formation are:Hf HO l   = -285.8 kJ/molHf H g   = 0 kJ/molHf O g   = 0 kJ/molNow, we can plug these values into the formula:H = [2   -285.8 kJ/mol ] - [2   0 kJ/mol  + 1   0 kJ/mol ]H =  -571.6 kJ/mol  -  0 kJ/mol H = -571.6 kJ/molThe standard enthalpy change for the reaction 2H g  + O g  -> 2HO l  is -571.6 kJ/mol.