Final answer:
When a gas dissolves in a liquid, the entropy of the system decreases because the gas molecules have fewer microstates available and become part of a more ordered system compared to the free state of the gas.
Step-by-step explanation:
For the dissolution of a gas in a liquid, the entropy change for the system (gas) decreases, which can be represented as ΔS < 0. Gas molecules have higher entropy due to their greater degrees of freedom (translational, rotational, vibrational) compared to liquid molecules. When gas molecules dissolve in a liquid, the system's entropy decreases because there are fewer gas molecules and thus fewer microstates available. This process results in a more ordered system with lower entropy.
Following the principle that entropy is higher for the gaseous state than for the liquid state, the dissolution of a gas into a liquid leads to a decrease in entropy for the gas as it becomes part of the liquid phase. This is in line with the general concept that dissolution increases entropy for solute dissolution in solvents, but in the specific case of a gas dissolving in a liquid, the transition from a state of higher freedom (gas) to lower freedom (liquid) leads to a decrease in entropy for the dissolved gas.