Adding Or Removing Thermal Energy From Water Causes It to Change State

February 14, 2024

The state of matter — solid, liquid or gas — changes when physical conditions change. Adding or removing heat causes the chemical bonding patterns and internal energy of water molecules to change. This is called a phase change. Heat energy can cause a substance to change states but does not change its temperature. This is because a change in state requires the addition or removal of a different type of energy, called latent heat.

The phase changes that can occur in water include evaporation, boiling, condensation, and sublimation. Evaporation is when liquid water turns into a gas, such as water vapor or steam. Boiling is the same as evaporation but happens at higher temperatures. Condensation is when the water vapor in the air turns back into liquid water, such as rain. Sublimation is the opposite of evaporation; it occurs when a solid turns directly into a gas without passing through the liquid phase.

In all of these processes, the water molecules are still composed of the same chemical elements. The difference is that the orientation of hydrogen bonds is different in each state. In a solid, the hydrogen bonds are closer together and this makes it more dense. In a liquid, the hydrogen bonds are farther apart and this makes it lighter. This is why water expands when it freezes, as you may have noticed if you’ve ever put a bottle of water in the freezer only to find it explodes as it expands. Most other liquids also expand when they freeze because the lowering of kinetic (movement) energy allows them to pack more tightly, which increases their density. Water is an exception to this rule because of its unique properties.


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