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Calculate the enthalpy of formation of O...

Calculate the enthalpy of formation of OH-ions at 25°C from the following thermochemical data:
`H _(2) O (l) to H ^(+) (aq) + OH ^(-) (aq) , Delta H ^(@) = 57.3 kJ`
`H _(2) (g) + 1//2 O _(2) (g) to H _(2) O (l) , Delta H ^(@) =- 258.9 kJ`

Text Solution

Verified by Experts

On addition of the above equations,
`H _(2) (g) + 1//2 O _(2) (g) to H ^(+) (aq) + OH ^(-) (aq) , Delta H ^(+) =- 228 . 6 kJ`
`Delta H =- 228. 6 kJ = 0 + Delta H _(f) ^(0) [OH ^(-) (aq) ] - (0+0) =- 228 . 6 kJ mol ^(-1)`
By convention, `Delta H _(f) ^(0) [ H ^(+) (aq) ] = 0.`
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