Calculate heat of formation of $\mathrm{SO}_2$ from following equations.

$$ \begin{aligned} & \mathrm{S}+\frac{3}{2} \mathrm{O}_2 \longrightarrow \mathrm{SO}_3, \Delta \mathrm{H}=-2 \mathrm{xkJ} \\ & \mathrm{SO}_2+\frac{1}{2} \mathrm{O}_2 \longrightarrow \mathrm{SO}_3, \Delta \mathrm{H}=-\mathrm{ykJ} \end{aligned} $$

Which of the following symbols represents heat of reaction at constant pressure?

The entropy of vaporisation of benzene is $85 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}$. When 117 g of benzene vaporises at its boiling point, what is entropy change of surrounding if process is at equilibrium?

Which from following terms is explained by first law of thermodynamics?