Question

which reaction results in a decrease in the entropy of the system? h₂o(g) → h₂o(l) kcl(s) → kcl(l) ch₃oh(l) → co(g) + 2h₂(g)

Explanation:

Entropy is a measure of disorder. For a reaction to decrease entropy, the system becomes more ordered.

• For \( \ce{H2O(g) -> H2O(l)} \): Gas to liquid (condensation) reduces disorder (gas molecules are more spread out than liquid), so entropy decreases.
• For \( \ce{KCl(s) -> KCl(l)} \): Solid to liquid (melting) increases disorder, so entropy increases.
• For \( \ce{CH3OH(l) -> CO(g) + 2H2(g)} \): Liquid to gases (more moles of gas), increases disorder, so entropy increases.

Thus, the reaction with decreased entropy is \( \ce{H2O(g) -> H2O(l)} \).

Answer:

A. \( \ce{H2O(g) -> H2O(l)} \)