States of Matter: Heating and Changes of State

Understand the three fundamental states of matter: solid, liquid and gas. Solids have a fixed shape and cannot flow, liquids can flow and fill the bottom of a container, and gases can spread out and fill any container.
Recognize atoms and particles in these three states. In solids, particles are closely packed in a fixed arrangement. In liquids, particles are close together but can move past each other. In gases, particles are far apart with a lot of space between them.
Understand that heating a solid, liquid or gas can make it change state. For example, heating a solid will usually turn it into a liquid (melting), while heating a liquid can turn it into a gas (evaporating).
Understand that cooling a gas, liquid or solid can also cause state changes. For example, cooling a gas can turn it into a liquid (condensation), and cooling a liquid can turn it into a solid (freezing).
Recognize that changes of state are physical changes, not chemical ones. The substance itself does not change, only its state does. This means that the process is usually reversible.
Understand that during changes of state, temperature does not change until the entire sample has converted to the other state. For example, during melting, the entire solid must first melt into a liquid before the temperature can increase.
Familiarize with the terms ‘endothermic’ and ‘exothermic’. Changes of state that absorb energy, such as melting and evaporating, are called endothermic changes. Changes that release energy, such as freezing and condensation, are called exothermic changes.
Understand that the heating curve graph shows the temperature change of a substance as it is heated and goes through phase changes. Its plateaus represent the change of phase, where the substance is absorbing or releasing heat but the temperature remains constant.