Represent the potential energy / enthalpy change in the following processes graphically.
$(a)$ Throwing a stone from the ground to the roof.
$(b)$ $\frac{1}{2} H_{2(g)} + \frac{1}{2} Cl_{2(g)} \rightarrow HCl_{(g)}$
In which of the processes is the potential energy/enthalpy change a contributing factor to the spontaneity?

(B) The graphical representation of potential energy/enthalpy change is as follows:
$(a)$ For throwing a stone from the ground to the roof,the potential energy of the stone increases as it moves against the gravitational field.
$(b)$ For the reaction $\frac{1}{2} H_{2(g)} + \frac{1}{2} Cl_{2(g)} \rightarrow HCl_{(g)}$,the enthalpy change is $\Delta_{r} H^{\ominus} = -92.32 \ kJ \ mol^{-1}$.
Energy increases in process $(a)$ and decreases in process $(b)$. $A$ decrease in enthalpy (exothermic process) generally favors spontaneity. Hence,in process $(b)$,the enthalpy change is a contributing factor to the spontaneity.