Question

Calculate the standard enthalpy of formation for propene (C3H6) given that the standard enthalpy of combustion of propene is -1411.1 kJ/mol and the standard enthalpy of formation of carbon dioxide (CO2) and water (H2O) are -393.5 kJ/mol and -285.8 kJ/mol respectively.

Answer 1

To calculate the standard enthalpy of formation for propene  C3H6 , we can use the following equation:Hf  propene  = Hc  propene  +  [Hf  products ] -  [Hf  reactants ]The balanced combustion reaction for propene is:C3H6 + 9/2 O2  3 CO2 + 3 H2OThe standard enthalpy of combustion of propene  Hc  is given as -1411.1 kJ/mol.The standard enthalpy of formation of CO2  Hf  is given as -393.5 kJ/mol, and for H2O  Hf  is -285.8 kJ/mol.Now, we can plug these values into the equation:Hf  propene  = -1411.1 kJ/mol + [3 -393.5 kJ/mol  + 3 -285.8 kJ/mol ] - [Hf  propene  + 0]Note that the standard enthalpy of formation for O2 is 0 since it is in its elemental form.Solving for Hf  propene :Hf  propene  = -1411.1 kJ/mol + [-1180.5 kJ/mol - 857.4 kJ/mol] - Hf  propene Combine the terms:2Hf  propene  = -1411.1 kJ/mol +  -2037.9 kJ/mol 2Hf  propene  = 626.8 kJ/molNow, divide by 2 to find the standard enthalpy of formation for propene:Hf  propene  = 313.4 kJ/molSo, the standard enthalpy of formation for propene  C3H6  is 313.4 kJ/mol.