Final answer:
The three phases of matter are solid, liquid, and gas. The state of a substance at a specific temperature is determined by the balance between particle energy and intermolecular forces. Observations of substances at different temperatures provide evidence for these ideas.
Step-by-step explanation:
The three phases of matter are solid, liquid, and gas. In the solid phase, particles are in contact with each other and held in place. In the liquid phase, particles are in contact but are able to move with respect to each other. In the gas phase, particles are separated from each other by large distances.
The state of a substance at a specific temperature depends on the balance between the energy of the particles and the intermolecular forces between them. If the forces between particles are strong, the substance is a liquid or a solid. If the forces between particles are weak and there is enough energy, the substance exists in the gas phase.
Evidence for these ideas comes from observations of substances at different temperatures. For example, water can exist as a solid (ice), liquid (water), or gas (water vapor) depending on the temperature. At low temperatures, the intermolecular forces are strong enough to hold the water molecules together in a solid state. As the temperature increases, the energy of the molecules increases and the forces between them weaken, allowing the molecules to move more freely and exist in the liquid phase. At even higher temperatures, the energy of the molecules is high enough to overcome the intermolecular forces completely, leading to the gas phase.