1.

In order to decompose 9g water 142.5 kJ heat is required. Hence the enthalpy of formation of water is

Answer»

`-285kJ`
`+285kJ`
`-142.5kJ`
`+142.5kJ`

Solution :`DELTA H = Sigma H_(("product"))^(0) - SigmaH_(("reactant"))^(0)`
`2H_(2)O rarr 2H_(2) + O_(2)`
`Delta H_(f) = 2 XX H_((O_(2)))^(0) -2 xx H_((H_(2)O))^(0)`
`=0 + 0-2 xx 142.5 = -285kJ`
`Delta H_(f)` for 1 MOLE of `H_(2)O = -142.5kJ`


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