SIMPLIFIED: "5.2: Phase Transitions"

Link to article: https://chem.libretexts.org/Courses/BridgeValley_Community_and_Technical_College/Consumer_Chemistry/05%3A_Solids_and_Liquids/5.02%3A_Phase_Transitions_-_Melting%2C_Boiling%2C_and_Subliming

Note: The image above was taken from the original article.

Matter is always changing to different states of matter. Ice melts into water, water boils into steam(gas), and frost can form on a cold window. Even though these are just a few examples, there are many more phase changes that happen. What are they?

When a solid becomes a liquid, the process is called melting. The opposite process, when a liquid becomes a solid, is called solidification or, more commonly, freezing. For example, ice melts into water at 0°C. Melting requires energy because the particles in a solid are tightly packed together, and energy is needed to take the tightly packed particles into more loosely packed positions. The energy needed to melt one mole of a substance is called the enthalpy of fusion. 

If more energy is added to a liquid, it can eventually become a gas through vaporization. When particles reach a certain point where they gain enough energy to separate and move freely, it is called the boiling point. 

The energy required to turn a liquid into a gas is called the enthalpy of vaporization. Unlike vaporization, condensation releases energy. 

Matter is also able to skip the liquid phase completely. This is called sublimation, and it occurs when a solid changes directly into a gas. The reverse process is called deposition. 

All of these phase changes are physical changes. The reason is that the substance itself remains the same; only the movement and arrangement of its particles change.