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In which of the following reactions At 2...

In which of the following reactions At `25^(@)C`, does the standard enthalpy change correspond to the standard enthalpy of formation of `H_(2)O(l)` ? Give reasons.
(i) `H_(2)(g) +(3)/(2)O_(3)(g) to H_(2)O(l)`
(ii) `H_(2)(g)+(1)/(2)O_(2)(g)toH_(2)O(l)`
(iii) `2H(g)+O_(2)(g) to H_(2)O(l)`.

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(i) The standard enthalpy change inthis reaction does not indicate the standard heat of formation of `H_(2)O(l)` because, the standard state of oxygen at `25^(@)C`, is `O_(2)(g) and ` not `O_(3)(g)`.
(ii) The standard enthalpy change in this reaction refers to the standard heat of formation of `H_(2)O(l)`, because 1 mol of `H_(2)O(l)` is formed from its stable constituent elements.
(iii) The standard enthalpy change in this reaction does not indicate the standard heat of formation of `H_(2)O(l)`. this is because of the fact that the stable state of hydrogen at `25^(@)C`, is not H(g).
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