Question

Calculate `Delta_(h)H^(ɵ)` for the addition of 1 mol of `H_2` to (i) benzene `(C_(6)H_(6))` and (ii) 1,3-cyclohexadiene `(C_(6)H_(8))` from frigure.
Strategy (i): Target is to find `Delta_(h)H^(ɵ)` of the following reaction benzene `+H_(2)to1,3-`Cyclohexadiene
Thus, look for the data involving these two compound.
strategy (ii). We need to find `Delta_(h)H^(ɵ)` of the following reaction:
`1,3-C_6H_8+H_2toC_6H_(12)`
Thus, we look for the data involving these two compounds.

Answer 1

(a). `C_(6)H_(6)+3H_2toC_(6)H_(12)`, `Delta_(h)H^(ɵ)=-208Kgmol^(-1)`
(b). `1.3-C_6H_6+2H_2toC_6H_(12)`, `Delta_(h)H^(ɵ)=-232kJmol^(-1)`
Substracting second equation (b) from the first (a), we get
`C_6H_6+H_2to1,3-C_6H_6`, `Delta_(h)H^(ɵ)24kJmol^(-1)`
(ii). (a). `1,3-C_6H_6+2H_2toC_6H_(12)toC_6H_(12)`, `Delta_(h)H^(ɵ)-232mol^(-1)`
(b). `C_6H_(10)+H_(2)toC_6H_(12)`, `Delta_(h)H^(ɵ)-120kJmol^(-1)`
Subtracting second equation (b) from the first (a), we get
`1,3-C_6H_8+H_2toC_6H_(10)`, `Delta_(h)H^(ɵ)112kJmol^(-1)`