GRE Subject Test: Chemistry : Entropy

Study concepts, example questions & explanations for GRE Subject Test: Chemistry

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Example Questions

Example Question #1 : Entropy

Which of the following reactions has a positive value for change in entropy ?

Possible Answers:

Water evaporates into water vapor

A salt precipitates out of a saturated solution

Water freezing into ice

Correct answer:

Water evaporates into water vapor


Entropy is a measure of the disorder of a system. In other words, when the components of a system become more uniform and spread out, the entropy of the system has increased. For example, when a liquid becomes gaseous, the molecules separate from one another, increasing the disorder of the system. As a result, the evaporation of water results in an increase in entropy.

All other options result in a more ordered system, which decreases entropy.

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