The bond enthalpies of heavy hydrogen $(D-D)$, oxygen $(O=O)$, and heavy water $(D-O)$ are $+400$, $+498$, and $+490 \ kJ \ mol^{-1}$, respectively. The $\Delta_{r} H^{\circ}$ of the reaction to produce $D_2O$ is:

If the heats of combustion of $C$,$S$,and $CS_2$ are $x$,$y$,and $z \, kJ \, mol^{-1}$ respectively,what will be the heat of formation of $CS_2$?

Hess's law of constant heat summation includes:

Calculate the standard enthalpy change of the following reaction:
$C_2H_{4(g)} + 3O_{2(g)} \longrightarrow 2CO_{2(g)} + 2H_2O_{(\ell)}$
Given:
$\Delta_{f}H^{\circ}(C_2H_4) = 52 \ kJ \ mol^{-1}$
$\Delta_{f}H^{\circ}(CO_2) = -393.5 \ kJ \ mol^{-1}$
$\Delta_{f}H^{\circ}(H_2O) = -285.8 \ kJ \ mol^{-1}$
(Note: Standard values adjusted for accuracy)

Which of the following is an endothermic reaction?

Which of the following values of heat of formation indicates that the product is least stable in $kcal$?