Chemistry Practice Problems Entropy Practice Problems Solution: Which of the following reactions will have a negat...

Solution: Which of the following reactions will have a negative value of ΔS?(i) Ba2+(aq) + SO42-(aq) → BaSO4(s)(ii) 2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g)(iii) 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(l)a. I and IIIb. I, II and IIIc. I and IId. II onlye. II and III

Problem

Which of the following reactions will have a negative value of ΔS?

(i) Ba2+(aq) + SO42-(aq) → BaSO4(s)

(ii) 2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g)

(iii) 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(l)

a. I and III

b. I, II and III

c. I and II

d. II only

e. II and III

Solution

We’re being asked to predict the sign of the entropy change (ΔS) for the given reactions:


(i) Ba2+(aq) + SO42-(aq)  BaSO4(s)

(ii) 2 Na(s) + 2H2O(l)  2 NaOH(aq) + H2(g)

(iii) 2 C2H6(g) + 7 O2(g)  4 CO2(g) + 6 H2O(l)


Recall that if:

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

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


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