Question

Assuming standard conditions, calculate the standard enthalpy of combustion of methane (CH4), given that the standard enthalpies of formation of CH4 and H2O are -74.8 kJ/mol and -285.8 kJ/mol, respectively. The balanced chemical equation for the combustion of CH4 is:CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) What is the standard enthalpy change (ΔH°) for this reaction?

Answer 1

To calculate the standard enthalpy change  H  for the combustion of methane, we can use the following equation:H =  Hf products  -  Hf reactants The standard enthalpy of formation  Hf  of O2 is 0 kJ/mol since it is in its elemental form. The standard enthalpy of formation of CO2 is -393.5 kJ/mol.Now, we can plug in the values into the equation:H = [1   -393.5 kJ/mol  + 2   -285.8 kJ/mol ] - [1   -74.8 kJ/mol  + 2  0 kJ/mol]H =  -393.5 - 571.6  -  -74.8 H = -965.1 + 74.8H = -890.3 kJ/molThe standard enthalpy change  H  for the combustion of methane is -890.3 kJ/mol.