Question

Calculate the change in enthalpy for the reaction CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l) given that the enthalpies of formation for CH4 (g), CO2 (g) and H2O (l) are -74.81 kJ/mol, -393.51 kJ/mol and -285.83 kJ/mol respectively.

Answer 1

To calculate the change in enthalpy  H  for the reaction, we can use the formula:H =  Hf products  -  Hf reactants where Hf represents the enthalpy of formation for each substance.For the given reaction, the reactants are CH4  g  and 2O2  g , and the products are CO2  g  and 2H2O  l .Hf CH4  = -74.81 kJ/molHf CO2  = -393.51 kJ/molHf H2O  = -285.83 kJ/molNow, we can plug these values into the formula:H = [1   -393.51 kJ/mol  + 2   -285.83 kJ/mol ] - [1   -74.81 kJ/mol  + 2  0 kJ/mol]Note that the enthalpy of formation for O2  g  is 0 kJ/mol because it is in its standard state.H =  -393.51 - 2  285.83 + 74.81  kJ/molH =  -393.51 - 571.66 + 74.81  kJ/molH = -890.36 kJ/molTherefore, the change in enthalpy for the reaction is -890.36 kJ/mol.