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The difference between the heats of reac...

The difference between the heats of reaction at constant pressure and a constant volume for the reaction `2C_(6)H_(6)(l) + 15O_(2)(g) rarr 12CO_(2)(g) + 6H_(2)O(l)` at `25^(@)C` in `kJ` is

A

`+ 7.43`

B

`- 3.72`

C

`- 7.43`

D

`+ 3.72`

Text Solution

Verified by Experts

The correct Answer is:
C
The thermochemical equation is
`2C_(6) H_(6) (1) + 15 O_(2) rarr 12 CO_(2) (g) + 6 H_(2) O (1)`
The heat of reaction at constant pressure is `Delta H` while the heat of reaction at constant volume is `Delta U`. According to thermodynamics.
`Delta H = Delta U + Delta n_(g) RT`
or `Delta H - Delta U = Delta n_(g) RT`
`Delta n_(g) sum n_(P) (g) - sum n_(R) (g)`
`= 12 - 15 = - 3`
Thus,
`Delta H - Delta U = (-3) (8.314) (298)`
`= - 7.43 kJ`
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