Question

15. Which forward reaction below indicates an entropy

decrease?
A) C6H6(S) + C6H6(1)
B) 2 IBr(g) + 12(s) + Brz(1)
C) NH4Cl(s) + NH3(g) + HCl(g)
D) (NH4)2CO3(s) + 2 NH3(g) + H2O(g) + CO2
E) NaCl(s) → Na+(aq) + CI-(aq)

Answer 1

The forward reaction that indicates an entropy decrease is B) 2 IBr(g) + I2(s) + Br2(l), as it results in a phase change from a gaseous state to a solid and liquid, therefore reducing disorder and the number of particles.

Step-by-step explanation:

The question asks which forward reaction indicates an entropy decrease. Entropy is a measure of the number of ways a system can be arranged, often associated with the randomness or disorder of particles. An entropy decrease typically occurs when a reaction results in fewer gas molecules, a phase change from a more chaotic to a more ordered state, or a reduction in the number of particles.

Option C) NH4Cl(s) → NH3(g) + HCl(g) indicates an entropy increase because it involves breaking up a solid into two gases, increasing the disorder. Option D) (NH4)2CO3(s) → 2 NH3(g) + H2O(g) + CO2 also indicates an entropy increase because a solid reacts to form more gas molecules.
Option E) NaCl(s) → Na+(aq) + Cl-(aq) represents an entropy increase for similarly converting a solid to more dispersed ions in solution. Therefore, by elimination, the correct answer, which indicates an entropy decrease, is B) 2 IBr(g) + I2(s) + Br2(l), as it involves converting gases into a solid and liquid, thus reducing the number of particles and the degree of disorder.