Physical Chemistry : Laws of Thermodynamics

Study concepts, example questions & explanations for Physical Chemistry

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Example Questions

Example Question #1 : Thermochemistry And Thermodynamics

A newly discovered element has been determined to have a standard entropy of  in its pure form. This value is highly unlikely because it violates the __________.

Possible Answers:

Second Law of Thermodynamics

First Law of Equivalent Exchange

Zeroth Law of Thermodynamics

First Law of Thermodynamics

Third Law of Thermodynamics

Correct answer:

Third Law of Thermodynamics


The Third Law of Thermodynamics states that a pure crystalline substance at absolute zero has an entropy of . Mathematically, this formula is expressed as:

where  is the Boltzmann constant  and W is the number of microstates of a gaseous atom in the system. Because microstates are used to describe this gaseous atom, there has to be at least one or more. 

If only one microstate exists for the system, then the entropy is zero , and can only increase from this point. It is therefore mathematically impossible for any element to have a negative standard entropy. 

Remark: keep in mind that entropy changes can be negative, but the entropy of pure compounds cannot be negative. 

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