As the temperature of a solid, liquid, or gas increases, particles move more rapidly. As the temperature drops, the particles slow down. If a liquid cools sufficiently, it forms a solid. If a liquid gets hot enough, it forms a gas.
Temperature has a direct effect on whether a substance exists as a solid, liquid, or gas. Generally, the increase in temperature turns solids into liquids and liquids into gases; when it decreases, gases become liquids and liquids become solids. The state of matter in a substance is an extrinsic property, meaning that its environment can change it. Physical conditions such as temperature and pressure affect the state of matter.
Both temperature and pressure can be measured and changes in state can be observed. The difference in temperatures and phases of different types of matter allows the operation of thermal engines and refrigerators. When energy is extracted, the opposite happens: it lowers the temperature of the substance and converts it from liquid to solid (freezing), from gas to solid (deposition) or from gas to liquid (condensation). When a substance is placed in a different temperature environment, heat is exchanged between the substance and the environment, causing both to reach an equilibrium temperature.
For this reason, ice melts if removed from the freezer and water boils from a pot if left at too high a temperature for too long. When a certain temperature threshold unique to each substance in the universe is crossed, a phase change occurs that changes the state of matter. The point at which matter subject to a particular temperature under conditions of constant pressure begins to change phase is called the phase change threshold. With all the information provided, it is only feasible for pressure and temperature to directly correspond to matter and the atomic phase change.
As temperatures increase, additional thermal energy is applied to the constituent parts of a solid, causing additional molecular movement. If the pressure is constant, the state of a substance will depend entirely on the temperature to which it is exposed. Temperature affects the phase change by slowing down the movement between atoms, which causes a change in kinetic energy, which in turn causes atoms to undergo forms of combination or some type of dispersion.
