2.3 Chemical Properties and Reactions

Chemical Properties and Reactions

States of Matter

Changes of State

Most substances can exist in either solid, liquid, or gas form, depending on temperature. At low temperatures, substances are solid. If the solid is heated, its atoms gain energy and begin to move more quickly, and it melts and forms a liquid. For example, when you add heat to a solid like ice, the ice melts, becoming water.

If the liquid is further heated until it boils, the atoms absorb even more energy. They move faster, and the liquid forms a gas. At very high temperatures, the electrons of an atom can separate from its nucleus, forming a fourth state of matter, plasma. The sun and other stars are made of plasma. 

Matter can also change from one state to another through removal of heat energy. When you take heat out of a substance, its atoms lose energy and their motion slows. For example, when you place water in a freezer, it loses energy and freezes.

This table summarizes the changes of state of matter.

A glass artist talks about manipulating glass from a solid to a liquid and back.