Methane gas, CH4(g), is combined with chlorine gas and fluorine gas to produce Freon-12 gas,
CF2Cl2(g).
The balanced chemical equation is:
CH4(g) + 2 Cl2(g) + 2 F2(g) → CF2Cl2(g) + 2 HF(g) + 2 HCl(g)
Reference bond energies:
C−H: 413 kJ/mol
Cl−Cl: 239 kJ/mol
F−F: 154 kJ/mol
C−F: 485 kJ/mol
C−Cl: 339 kJ/mol
H−F: 565 kJ/mol
H−Cl: 427 kJ/mol
Calculate the enthalpy change (Show all steps, work, units and a concise final answer)
To calculate the enthalpy change (ΔH) for the reaction, we need to determine the total energy absorbed and released during the reaction. This can be done by summing up the bond energies of the reactants and the products.
Reactants:
CH4(g) + 2 Cl2(g) + 2 F2(g)
Products:
CF2Cl2(g) + 2 HF(g) + 2 HCl(g)
Calculating the energy absorbed:
4 × C−H bonds × (413 kJ/mol) = 1652 kJ/mol
2 × Cl−Cl bonds × (239 kJ/mol) = 478 kJ/mol
2 × F−F bonds × (154 kJ/mol) = 308 kJ/mol
Total energy absorbed = 1652 kJ/mol + 478 kJ/mol + 308 kJ/mol = 2438 kJ/mol
Calculating the energy released:
2 × C−F bonds × (485 kJ/mol) = 970 kJ/mol
1 × C−Cl bond × (339 kJ/mol) = 339 kJ/mol
2 × H−F bonds × (565 kJ/mol) = 1130 kJ/mol
2 × H−Cl bonds × (427 kJ/mol) = 854 kJ/mol
Total energy released = 970 kJ/mol + 339 kJ/mol + 1130 kJ/mol + 854 kJ/mol = 3293 kJ/mol
ΔH = Total energy absorbed - Total energy released
= 2438 kJ/mol - 3293 kJ/mol
= -855 kJ/mol
Therefore, the enthalpy change for the reaction is -855 kJ/mol.