What Is a Phase Change in Science?

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A phase change in science refers to any substance that changes from one state to another, with possible states being gas, liquid and solid. Substances typically phase change to the closest related state, such as liquid to solid, but in certain conditions can go from gas to solid or solid to gas.

Each phase represents a quantity of energy. The more energy that a substance contains, the more likely that individual molecules or atoms will be able to resist intermolecular forces and spread apart. There are three main phases a substance can exist in:

  • Gas: The most energetic form of a substance. Molecules in the gas phase are able to move around with a lot of free space and rarely bump into each other.
  • Liquid: Molecules have enough energy to rotate, vibrate and move around a bit. Substances in a liquid form can flow at varying speeds depending on their viscosity.
  • Solid: The most stable form where molecules are packed tightly together. There is little movement between molecules due to them having a small amount of energy.

One way for a substance to change phase to occur is to add energy to it or take it away. This can be done directly through the application of heat or electricity. Another way is to manipulate the variables of the environment. A high pressure environment forces molecules together, which favors liquid and solid forms. Similarly, a small volume or container also favors molecules being close together.