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The standard enthalpies of formation of ...

The standard enthalpies of formation of `CO_(2)(g), H_(2)O(l)` and glucose(s) at `25^@C` are `-400 kJ//mol, -300 kJ//mol and -1300 kJ//mol` respectively. The standard enthalpy of combustion per gram of glucose at `25^@C` is :

A

`+2900` KJ

B

`-2900` KJ

C

`-16.11` KJ

D

`+16.11 `KJ

Text Solution

Verified by Experts

The correct Answer is:
C
`C_(6)H_(12)O_(6)(g) rarr 6CO_(2)(g) + 6H_(2)O(l)`
`Delta_(c)H = 6 xx Delta_(f)H(CO_(2)) + 6 Delta_(f)H (H_(2)O) - Delta_(f)H(C_(6)H_(12)O_(6)) - 6Delta_(f)(O^(2),g)`
`=6 xx (-400-300) - (-1300)-0`
`=-4200 + 1300`
=-2900KJ/mol
For one gram of glucose, enthalphy of combustion `=-(2900)/(180) =-16.11 kJ//g`
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