From the following data, the heat of formation of `Ca(OH)_(2)(s)` at `18^(@)C` is …. Kcal. (i) `CaO(s)+H_(2)O(l)=Ca(OH)_(2)(s) , Delta H18^(@)C=-15.26` Kcal….. (ii) `H_(2)O(l)=H_(2)(g)+1//2O_(2)(g) , Delta H18^(@)C=68.37` Kcal…. (iii) `Ca(s)+1//2O_(2)(g)=CaO(s) , Delta H 18^(@)C=-151.80` Kcal....A. `-98.69`B. `-235.43`C. `194.91`D. `98.69`

From the following data, the heat of formation of `Ca(OH)_(2)(s)` at `

1.	From the following data, the heat of formation of `Ca(OH)_(2)(s)` at `18^(@)C` is …. Kcal. (i) `CaO(s)+H_(2)O(l)=Ca(OH)_(2)(s) , Delta H18^(@)C=-15.26` Kcal….. (ii) `H_(2)O(l)=H_(2)(g)+1//2O_(2)(g) , Delta H18^(@)C=68.37` Kcal…. (iii) `Ca(s)+1//2O_(2)(g)=CaO(s) , Delta H 18^(@)C=-151.80` Kcal....A. `-98.69`B. `-235.43`C. `194.91`D. `98.69`
Answer» Correct Answer - B `Ca_((s))+O_(2(g))+H_(2(g))rarr Ca(OH)_(2) , Delta H_(f) = ?` Desired equation = eq (iii) + eq(i) - eq (ii) `Delta H_(f)=(-151.80)+(-15.26)-(-68.37)` `Delta H_(f)=-235.43 KCal mol^(-1)`

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