Question

The standard enthalpies of combustion of `C_(6)H_(6) (l) ` ,C ( graphite) and`H_(2)(g)` are respectively `-3270 kJ mol^(-1), - 394kJ mol^(-1)` and`-286 kJmol^(-1)` . What is the standard enthalpy of formation of`C_(6)H_(6)(l)`in `kJ mol^(-1)` /
A. `- 48`
B. `+48`
C. `-480`
D. `+480`

Answer 1

Correct Answer - b
(i) ` C_(6)H_(6)+ ( 15)/(2) O_(2) rarr 6CO_(2)+3H_(2) O, DeltaH= - 3270 kJ mol^(-1)`
(ii) `C+ O_(2) rarr CO_(2), DeltaH = -394kJ mol^(-1)`
(iii) `H_(2)+(1)/(2) O_(2) rarr H_(2)O,DetlaH=-286kJ mol^(-1)`
Aim `: 6C+ 3H_(2) rarr C_(6)H_(6) , DeltaH=?`
`6 xx`Eqn. (ii) `+ 3 xx ` Eqn. (iii) -Eqn. (i) ,gives required eqn.with `DeltaH =+ 48 kJ mol^(-1)`