The enthalpy change for the transition of carbon from diamond to graphite is $\Delta H = -453.5 \ \text{cal}$. What does this indicate?

For the reaction $\frac{1}{2} X_2O_{(s)} \to X_{(s)} + \frac{1}{4} O_{2(g)}$ with $\Delta H = 90 \ kJ$,the enthalpy change for the reaction of $1 \ mol$ of $O_2$ with metal $X$ is ................ $kJ$.

Given: $S + O_2 \rightarrow SO_2 : \Delta H_1 = -298.2 \ kJ$,$SO_2 + 1/2 \ O_2 \rightarrow SO_3 : \Delta H_2 = -98.7 \ kJ$,$SO_3 + H_2O \rightarrow H_2SO_4 : \Delta H_3 = -130.2 \ kJ$,and $H_2 + 1/2 \ O_2 \rightarrow H_2O : \Delta H_4 = -287.3 \ kJ$. Calculate the heat of formation of $H_2SO_4$ in $kJ$.

In the reaction $S + \frac{3}{2} O_{2} \rightarrow SO_{3} + 2x \ kJ$ and $SO_{2} + \frac{1}{2} O_{2} \rightarrow SO_{3} + y \ kJ$,the heat of formation of $SO_{2}$ is

Which of the following has a standard enthalpy of formation equal to zero?

For the reaction $H_{2} + I_{2} \rightarrow 2 HI$,provide the potential energy profile diagram and prove that it is an exothermic reaction.