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on the basis of the following thermochem...

on the basis of the following thermochemical data ` [Delta_(f) G^(@) H ^(+) (aq) = 0]`
` H_(2) O (1) to H ^(+) (aq) + O H ^(-) (aq), DeltaH = 57. 3 2 K J`
`H_(2) (g) + 1/2 O_(2) (g) to H_(2) O (I), DeltaH = -2 8 6 .2 0 K J` The value of enthalpy of formation of ` O H ^(-)` ion at `25^@C` is

A

`+228.88 kJ`

B

`-343.52 kJ`

C

`-22.88 kJ`

D

`-228.88 kJ`

Text Solution

Verified by Experts

The correct Answer is:
D
`H_(2)O_((l))rarr H^(+)(aq)+OH^(-)(aq) , Delta H=57.32`
`Delta H=[Delta H_(f)(H^(+))+Delta H_(f)(OH^(-)]-Delta H_(f)(H_(2)O)`
From eq. (ii) `Delta H_(f)(H_(2)O)=-286.20 kJ`
Given `Delta H_(f)(H^(+)) = 0`
`therefore 57.32 =0+Delta H_(f)(OH^(-))-(-286.20)`
`Delta H_(f)=-228.88 kJ`
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