ΔHrxn = ΣΔH breaking - ΣΔH making
CH₃CH₂OH(g) + HCl(g) →CH₃CH₂Cl(g) + H₂O(g)
the reaction equation is already balanced.
when we look at the equation, the bonds which break are C-O bond and H-Cl bond. The bonds which form are C-Cl bond and O-H bond.
Hence,
ΔHrxn = ΣΔH breaking - ΣΔH making
= (ΔH(C-O) + ΔH(H-Cl)) - (ΔH(C-Cl) + ΔH(O-H))
= ((358 + 427) - (339 + 467) kJ/mol
= -21 kJ/mol
