Question

consider the reaction cl₂(g) + br₂(g) → 2 brcl(g) at 25 °c. which of the following best explains why the change in entropy is so small? a all of the components in the chemical equation are gases. b there are the same moles of gas on both sides of the reaction. c the temperature of the reaction does not change.

Explanation:

To determine why the entropy change is small, we analyze each option:

• Option A: Just being gases doesn't explain small entropy change. Entropy change in gas reactions depends on moles of gas.
• Option B: The reaction has 1 mole of \( \text{Cl}_2 \) (gas) + 1 mole of \( \text{Br}_2 \) (gas) = 2 moles of \( \text{BrCl} \) (gas). So moles of gas on reactant side (\( 1 + 1 = 2 \)) and product side (2) are equal. Entropy change (\( \Delta S \)) is related to change in moles of gas (\( \Delta n_{\text{gas}} \)). If \( \Delta n_{\text{gas}} = 0 \), \( \Delta S \) is small as there's little change in disorder (since moles of gas don't change).
• Option C: Temperature being constant doesn't directly relate to the magnitude of entropy change for this reaction. Entropy change here is about moles of gas, not temperature (temperature affects absolute entropy, but the change here is about moles).

Answer:

B. There are the same moles of gas on both sides of the reaction.