The entropy change can be calculated by using the expression $\Delta S=\frac{q_{\text {rev }}}{T} \cdot$ When water freezes in a glass beaker, choose the correct statement amongst the following.

On the basis of theromochemical equations (1), (2) and (3), find out which of the algebraic relationships given in options (a) to (d) is correct

1. C (graphite) $+\mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{CO}_2(\mathrm{~g}) ; \Delta_r H=x \mathrm{~kJ} \mathrm{~mol}^{-1}$

2. C (graphite) $+\frac{1}{2} \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{CO}(\mathrm{g}) ; \Delta_r H=y \mathrm{~kJ} \mathrm{~mol}^{-1}$

3. $\mathrm{CO}(\mathrm{g})+\frac{1}{2} \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{CO}_2(\mathrm{~g}) ; \Delta_r H=z \mathrm{~kJ} \mathrm{~mol}^{-1}$

Consider the reactions given below. On the basis of these reactions find out which of the algebraic relationship given in options (a) to (d) is correct?

1. $\mathrm{C}(\mathrm{g})+4 \mathrm{H}(\mathrm{g}) \rightarrow \mathrm{CH}_4(\mathrm{~g}) ; \Delta_r H=x \mathrm{~kJ} \mathrm{~mol}^{-1}$

2. C (graphite) $+2 \mathrm{H}_2(\mathrm{~g}) \rightarrow \mathrm{CH}_4(\mathrm{~g}) ; \Delta_r H=y \mathrm{~kJ} \mathrm{~mol}^{-1}$

The enthalpies of elements in their standard states are taken as zero. The enthalpy of formation of a compound

Enthalpy of sublimation of a substance is equal to