 # Energy and Entropy

Entropy is a measure of the random activity in a system. The entropy of a system depends on your observations at one moment. How the system gets to that point doesn't matter at all. If it took a billion years and a million different reactions doesn't matter. Here and now is all that matters in entropy measurements.

When we say random, we mean energy that can't be used for any work. It's wild and untamed. Scientists use the formula (delta)S = (delta)Q /(delta)T. "S" is the entropy value, "Q" is the measure of heat, and "T" is the temperature of the system measured in Kelvin degrees. When we use the symbol delta, it stands for the change. Delta T would be the change in temperature (the original temperature subtracted from the final).

# Affecting Entropy

Several factors affect the amount of entropy in a system. If you increase temperature, you increase entropy.

(1) More energy put into a system excites the molecules and the amount of random activity.

(2) As a gas expands in a system, entropy increases. This one is also easy to visualize. If an atom has more space to bounce around, it will bounce more. Gases and plasmas have large amounts of entropy when compared to liquids and solids.

(3) When a solid becomes a liquid, its entropy increases.

(4) When a liquid becomes a gas, its entropy increases. We just talked about this idea. If you give atoms more room to move around, they will move. You can also think about it in terms of energy put into a system. If you add energy to a solid, it can become a liquid. Liquids have more energy and entropy than solids.

(5) Any chemical reaction that increases the number of gas molecules also increases entropy. A chemical reaction that increases the number of gas molecules would be a reaction that pours energy into a system. More energy gives you greater entropy and randomness of the atoms.   Or search the sites for a specific topic. Taking Earth’s Temperature (NASA Video) Physics4Kids: Thermodynamics
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