Question

From the following data, calculate the enthalpy change for the combustion of cyclopropane at `298K`. The enthalpy of formation of `CO_(2(g)),H_(2)O_((l))` and `Propen e_((g))` are `-393,-285.8` and ` 20.42 kJ mol^(-1)` respectively. The enthalpy of isomerisation of cyclopropane to propene is `-33.0kJ mol^(-1)`

Answer 1

Correct Answer - `2091.32 kJ mol^(-1)`
following equation can be obtained from the avilable data
(i) `C (s) + O_(2) (g) rarr CO_(2) (g) , Delta H = 393.5 kJ`
(ii) `H_(2) (g) + (1)/(2) O_(2) (g) rarr H_(2) O (l) , Delta H = 2858 kJ`
(iii) `3C (s) + 3H_(2) (g) rarr C_(2)H_(6) (g), Delta H = + 20.42 kJ`
`(g) rarr C_(3) H_(6) (g) , Delta H = -33.0 kJ`
The desired equation is
`(g) + (9)/(2) O_(2) (g) rarr 3 CO_(2) (g) + 3H_(2)O(l), Delta H = 2091.32 kJ mol^(-1)`
To get the desired equation compute as follows `[3 xx (i) + 3 xx (ii) ] + (vi) - (iii)]`

`(g) + (9)/(2)O_(2) (g) rarr 3CO_(2) (g) + 3H_(2)O (l)`,
`Delta H = 2091.32 kJ mol^(-1)`