Question

Calculate the standard enthalpy change of the reaction NH3(g) + 2O2(g) → NO2(g) + 3H2O(l) at 25°C, given that the standard enthalpies of formation of NH3(g), O2(g), NO2(g) and H2O(l) are -46.11 kJ/mol, 0 kJ/mol, 33.18 kJ/mol and -285.8 kJ/mol, respectively.

Answer 1

To calculate the standard enthalpy change of the reaction, we can use the formula:H =  Hf products  -  Hf reactants where H is the standard enthalpy change of the reaction, and Hf is the standard enthalpy of formation of the respective substances.For the given reaction:NH3 g  + 2O2 g   NO2 g  + 3H2O l The standard enthalpies of formation are:NH3 g : -46.11 kJ/molO2 g : 0 kJ/molNO2 g : 33.18 kJ/molH2O l : -285.8 kJ/molNow, we can plug these values into the formula:H = [ 1  33.18  +  3  -285.8 ] - [ 1  -46.11  +  2  0 ]H = [33.18 - 857.4] -  -46.11 H = -824.22 + 46.11H = -778.11 kJ/molSo, the standard enthalpy change of the reaction is -778.11 kJ/mol.