Answer:
ΔHºrxn = - 440 kJ
Explanation:
What we need to remember in this question is that given the bond energies for a reaction, the enthalpy change , ΔHº , is given by the expression:
ΔHºrxn = ∑ energies of the bonds broken - ∑ energies of the bonds formed.
where s ∑ is summatory.
The reaction is CH₄(g) + 4 Cl₂(g) ⇒ CCl₄(g) + 4 HCl(g)
So lets make the inventory of the bond broken and bonds formed
Bonds Broken:
4 C-H = 4 mol (413 kJ/mol ) = 1652 kJ
4 Cl-Cl = 4 mol ( 243 kJ/mol = 972 kJ/mol
Bond Formed:
4 C-Cl = 4 mol (339 kJ/mol ) = 1356 kJ
4 H-Cl = 4 mol (427 kJ/mol ) = 1708 kJ
Now we can calculate ΔHºrxn :
ΔHºrxn = ∑ energies of the bonds broken - ∑ energies of the bonds formed
ΔHºrxn = ( 1652 + 972 ) kJ - ( 1356 + 1708 ) kJ
= 2624 kj - 3064 kJ
= - 440 kJ
