Chemistry Practice Problems Entropy Practice Problems Solution: Which of the following result(s) in a decrease in ...

Solution: Which of the following result(s) in a decrease in the entropy of the system? I. NH3(1 atm, 298 K) → NH3(3 atm, 298 K) II. Br2(g) → Br2(l) III. NaBr(s) → Na+(aq) + Br-(aq) IV. O2(g, 298 K) → O2(g, 373 K) a. I, IIb. II onlyc. I and IIId. II and IIIe. III only

Problem

Which of the following result(s) in a decrease in the entropy of the system? 

I. NH3(1 atm, 298 K) → NH3(3 atm, 298 K) 

II. Br2(g) → Br2(l) 

III. NaBr(s) → Na+(aq) + Br-(aq) 

IV. O2(g, 298 K) → O2(g, 373 K) 

a. I, II

b. II only

c. I and III

d. II and III

e. III only

Solution

We’re being asked to predict which has the greatest entropy (ΔS) for the given reactions. Recall that if:

• ΔS > 0 or ΔS = (+); entropy is increased

• ΔS < 0 or ΔS = (–); entropy is decreased


Remember that phase changes lead to a change in entropy:

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