If the bond dissociation energies of $XY$,$X_2$,and $Y_2$ (all diatomic molecules) are in the ratio of $1 : 1 : 0.5$ and $\Delta_f H$ for the formation of $XY$ is $-200 \ kJ \ mol^{-1}$,the bond dissociation energy of $X_2$ will be in $kJ \ mol^{-1}$:

The total enthalpy change in a chemical reaction is equal to the algebraic sum of the enthalpy changes of the individual steps of the reaction. This statement is associated with which scientist?

Given the following thermochemical equations:
$(1) \ S + O_2 \rightarrow SO_2 ; \Delta H = -298.2 \ kJ$
$(2) \ SO_2 + \frac{1}{2} O_2 \rightarrow SO_3 ; \Delta H = -98.7 \ kJ$
$(3) \ SO_3 + H_2O \rightarrow H_2SO_4 ; \Delta H = -130.2 \ kJ$
$(4) \ H_2 + \frac{1}{2} O_2 \rightarrow H_2O ; \Delta H = -287.3 \ kJ$
Calculate the enthalpy of formation of $H_2SO_4$ at $298 \ K$ in $kJ$.

The heats of formation of $CO_2$ and $H_2O$ are $-97 \, kcal$ and $-68 \, kcal$ respectively. The heat of combustion of benzene is $-783 \, kcal$. What is the heat of formation of benzene in $kcal$?

Which of the following reactions is not exothermic?

Energy required to dissociate $16 \ g$ of oxygen gas $(O_2)$ into free atoms is $x \ kJ$. The heat of atomisation of oxygen is: