The standard heat of formation of sodium ions in aqueous solution from the following data :
Heat of formation of `NaOH(aq)` at `25^(@)C = - 470.7 KJ` :
Heat of formation of `OH^(-1)` at `25^(@)C = -228.8 KJ` is :

Options

A. `-251.9KJ`
B. 241.9KJ
C. `-241.9KJ`
D. `300KJ mol^(-1)`

Answer

C

Explanation

Reaction for heat of formation of sodium ions in aqueous solution is `Na_((s)) + H_(2)O_((aq)) rarr Na_((aq))^(+) + e^(-)` …(1)
Heat formation of `NaOH_((aq))`
`Na_((s)) + (1)/(2) O_(2(g)) + (1)/(2)H_(2(g)) rarr Na_((aq))^(+) + OH_((aq))^(-)` ...(2)
`(1)/(2) H_(2) + (1)/(2) O_(2) + e^(-) rarr OH_((aq))^(-)` ..(3)
Eq (1) = Eq.(2) - Eq.(3)
`Delta H = -470.7 - (-228.8) = -241. 9KJ`