If the value of $\Delta H$ in a reaction is positive,then the reaction is called

Calculate the heat of formation of $PCl_{5(s)}$ from the following data:
$2P_{(s)} + 3Cl_{2(g)} \to 2PCl_{3(l)}; \Delta H_1 = -151.8 \ kcal$
$PCl_{3(l)} + Cl_{2(g)} \to PCl_{5(s)}; \Delta H_2 = -32.8 \ kcal$
Determine the enthalpy of formation for $PCl_{5(s)}$ in $kcal$.

Which of the following reactions can be used to define the standard enthalpy of formation of $CO_{2_{(g)}}$?

Calculate the amount of methane formed by the liberation of $149.6 \ kJ$ of heat using the following equation:
$C_{(s)} + 2H_{2(g)} \longrightarrow CH_{4(g)} \quad \Delta H = -74.8 \ kJ/mol$ (in $g$)

The correct order of $\Delta_{f} H^{\circ}$ values of Diamond $(I)$, Graphite $(II)$, and Fullerene $(III)$ is:

The $\Delta H_f^{\circ}$ values (in $kJ \ mol^{-1}$) for graphite, diamond, and $C_{60}$ are respectively: