Phase transitions refer to the changes that occur when a substance shifts from one state of matter to another, such as from solid to liquid or liquid to gas. These transitions happen at specific temperatures and pressures, known as melting points and boiling points. For example, when ice (solid) is heated, it absorbs energy and eventually transforms into water (liquid). During a phase transition, the physical properties of a substance change significantly, but its chemical composition remains the same. This process involves the breaking or forming of bonds between molecules. Common examples include the freezing of water into ice and the condensation of steam back into liquid water.