(i) What do you mean by standard enthalpy of formation?
(ii) Is the standard enthalpy of reaction of the following reaction equal to the standard enthalpy off formation of `H_(2)O(l)` at `25^(@)C:H_(2)(g)+(1)/(3)O_(3)(g)toH_(2)O(l)` ? Explain.

Which of the following reaction does not define standard enthalpy of formation (Delta H_f^@) ?

Which of the following reactions do(es)n't represent the standard state enthalpy of formation reaction?

At 25^(@) C, is the standard reaction enthalpy for the reaction 2H(g) +O(g)toH_(2)O(l) the same as the standard enthalpy of formation of H_(2)O(l) ?

For which of the following reactions does the standard enthalpy of reaction represent the standard enthalpy of formation of CH_(4)(g) ? Explain it. (a) C(diamond, s) +4H_(2)(g)toCH_(4)(g) (b) C(graphite, s) +O_(2)(g)toCH_(4)(g) .

In which of the following reactions the standard heat of reaction is equal to the standard heat of formation of CaBr_(2)(s) at 25^(@)C ? (i) Ca(s)+Br_(2)(l)toCaBr_(2)(s) (ii) Ca(s)+Br_(2)(g)toCaBr_(2)(g) .

In which of the following standard enthalpy of formation (Delta H_(f)^(0)) is zero ?

What do you mean by the standard enthalpy of atomisation of chlorine at 25^(@)C=+121kJ*mol^(-1) ?

Give an example of a combustion reaction whose standard enthalpy change in equal to the standard enthalpy of formation of the compound formed in the reaction.

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) .

At 25^(@)C , in which of the given reactions do standard enthalpies of reactions indicate standard enthalpies of formation of the product in the respective reactions-