Predict the sign of ΔS for each of the following and...

Predict the sign of $\Delta S$ for each of the following and explain.
a. the evaporation of alcohol
b. the freezing of water
c. compressing an ideal gas at constant temperature
d. dissolving $\mathrm{NaCl}$ in water

Key Concepts

Dissolution and Mixing

Dissolution involves the process of a solid solute dispersing into a solvent, often resulting in an increase in entropy due to the mixing and distribution of solute particles throughout the solvent. This process typically increases the disorder in the system, even though interactions such as solvation can locally order solvent molecules.

Volume Effects on Entropy in Gases

For systems like an ideal gas, entropy is closely related to the volume available to the molecules. When a gas is compressed at constant temperature, the available space for molecular movement decreases, reducing the number of accessible microstates and thereby decreasing the entropy.

Phase Transitions

Phase transitions, such as evaporation and freezing, involve changes in the state of matter that typically affect disorder. In a transition from liquid to gas, the increased molecular freedom leads to a higher entropy. Conversely, transitioning from a liquid to a solid typically means that molecules become more ordered, resulting in a decrease in entropy.

Entropy

Entropy is a measure of the disorder or randomness in a system. It quantifies the number of microscopic configurations corresponding to the macroscopic state, with higher entropy indicating a higher level of disorder. Changes in entropy during physical or chemical processes help determine the spontaneity of those processes.

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