Question

What is the standard enthalpy change for the reaction 2NO(g) + O2(g) ⟶ 2NO2(g) , given that the standard enthalpy of formation of NO(g), O2(g) and NO2(g) are 90.4 kJ/mol , 0 kJ/mol, and 33.2 kJ/mol, respectively?

Answer 1

To calculate the standard enthalpy change for the reaction, we can use the formula:H reaction  =  Hf products  -  Hf reactants where Hf represents the standard enthalpy of formation of each substance.For the given reaction:2NO g  + O2 g   2NO2 g The standard enthalpy of formation for each substance is:NO g  = 90.4 kJ/molO2 g  = 0 kJ/molNO2 g  = 33.2 kJ/molNow, we can plug these values into the formula:H reaction  = [2  33.2 kJ/mol  NO2 ] - [2  90.4 kJ/mol  NO  + 0 kJ/mol  O2 ]H reaction  =  66.4 kJ/mol  -  180.8 kJ/mol H reaction  = -114.4 kJ/molThe standard enthalpy change for the reaction is -114.4 kJ/mol.