Question

What is the heat of formation (in kJ/mol) of methane (CH4) from its elements carbon (C) and hydrogen (H2) at standard conditions (25°C and 1 atm)? Use the following data for the bond energies: C-H = 414 kJ/mol, H-H = 436 kJ/mol, and C-C = 348 kJ/mol.

Answer 1

To calculate the heat of formation of methane  CH4  from its elements carbon  C  and hydrogen  H2 , we can use the bond energy data provided. The heat of formation is the difference between the energy required to break the bonds in the reactants and the energy released when the bonds in the products are formed.Methane  CH4  has 4 C-H bonds. The formation of one molecule of CH4 requires breaking one H-H bond in H2 and forming four C-H bonds in CH4.Energy required to break 1 H-H bond = 436 kJ/molEnergy released when forming 1 C-H bond = 414 kJ/molHeat of formation of CH4 =  Energy required to break bonds in reactants  -  Energy released when forming bonds in products Heat of formation of CH4 =  1 * 436 kJ/mol  -  4 * 414 kJ/mol Heat of formation of CH4 = 436 kJ/mol - 1656 kJ/molHeat of formation of CH4 = -1220 kJ/molThe heat of formation of methane  CH4  from its elements carbon  C  and hydrogen  H2  at standard conditions  25C and 1 atm  is -1220 kJ/mol.