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Topic: [Freshman Chem Thermochemistry] CLEP Study Guide Question  (Read 309 times)

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Offline digisol

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[Freshman Chem Thermochemistry] CLEP Study Guide Question
« on: February 04, 2020, 11:05:51 AM »
I am helping someone study for a CLEP test using a book of practice problems with answers. I'm struggling to understand the answer given for this problem:

Which is NOT true for entropy in a closed system according to the equation Δ S=Q/T?

A. Entropy is a measure of energy dispersal in the system

B. Equation is only valid for a reversible process

C. Changes due to heat transfer are greater at low temperatures

D. Disorder of a system decreases as heat is transferred out of the system

E. Increases as temperature decreases

They give the answer as C, with this explanation:

The equation relates to the change in entropy ( Δ S) at different temperatures. Entropy increases at higher temperatures (i.e. increased kinetic energy).

​To me, it seems like C and E say the same thing, and that both are true, hence neither would be the correct answer. A, B, and D also seem to be true, so there would be no correct answer given among the choices. Am I missing something?

Offline mjc123

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Re: [Freshman Chem Thermochemistry] CLEP Study Guide Question
« Reply #1 on: February 05, 2020, 08:14:42 AM »
C and E certainly do not say the same thing. E is talking about entropy, C is talking about entropy CHANGE. This is a VERY important distinction (for other quantities too, not just entropy) which you must clearly grasp to get anywhere in thermodynamics.

Entropy increases at higher temperatures, so E is wrong.
Entropy CHANGE due to heat transfer, by the equation ΔS = Q/T, is greater at lower temperatures for a given Q. So C is true.

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