Entropy - IB Physics Definition

In IB Physics, the entropy of a given system is a measure of the number of possible arrangements of the particles and their energies. In other words, it is a measure of how disordered a system is.

When a system becomes more disordered, its entropy will increase. The order of entropy for the different states of matter, from most disordered to least is:

gas > liquid > solid

The entropy of a substance changes during a change in state.

Entropy increases when a substance melts (solid → liquid) or boils (liquid → gas) . The particles in a gas can freely move around and are far apart from each other, and the entropy increases as the particles become more disordered.

Similarly, entropy decreases when a substance condenses (gas → liquid) or freezes (liquid → solid). The particles are brought together and become arranged more regularly, hence the entropy decreases.

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