Indicate which substance posses the larger standard entropy?

Updated on August 6, 2022

I have all of the answers, I am just not clear on the logic of finding them. Would someone explain it to me please?

“For each of the following pairs, indicate which substance possesses the larger standard entropy:”

A) 1 mol of P4 (g) at 300 ∘C, 0.01 atm; or 1 mol of As4 (g) at 300 ∘C, 0.01 atm

**answer: 1 mol of As4 (g) at 300 ∘C, 0.01 atm**

B) 1 mol of H2O (g) at 100 ∘C, 0.01 atm; or 1 mol of H2O (L) at 100 ∘C, 0.01 atm

**answer: 1 mol of H2O (g) at 100 ∘C, 0.01 atm

C) 0.5 mol of N2 (g) at 298 K, 20-L volume; or 0.5 mol C2H4 (g) at 298 K, 20-L volume

**answer: 0.5 mol C2H4 (g) at 298 K, 20-L volume

D) 100 g Na2SO4 (s) at 30 ∘C; or 100 g Na2SO4 (aq) at 30 ∘C

**answer: 100 g Na2SO4 (s) at 30 ∘C **

1 Answer

  • A) Mr P4 = 124 < Mr As4 = 300 , hence As4 has higher entropy

    B) Gas has higher entropy than liquid, and liquid has higher entropy than solid.

    C) Mr N2 = 14 < Mr C2H4 = 28, hence C2H4 has higher entropy

    D) It should be aqueous, not solid. Solid has less entropy than liquid, and liquid has less entropy than aqueous.

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