Question:
For the reaction,
$2 \mathrm{Cl}_{(g)} \rightarrow \mathrm{Cl}_{2(g)}$, what are the signs of $\Delta \mathrm{H}$ and $\Delta \mathrm{S}$ ?
Solution:
$\Delta H$ and $\Delta S$ are negative
The given reaction represents the formation of chlorine molecule from chlorine atoms. Here, bond formation is taking place. Therefore, energy is being released. Hence, $\Delta H$ is negative.
Also, two moles of atoms have more randomness than one mole of a molecule. Since spontaneity is decreased, $\Delta S$ is negative for the given reaction.