Phase Change: Evaporation, Condensation, Freezing, Melting, Sublimation & Deposition.

Phase Changes

Phase changes require either the addition of heat energy (melting, evaporation, and sublimation) or subtraction of heat energy (condensation and freezing). Changing the amount of heat energy usually causes a temperature change.

A phase change is a physical process in which a substance goes from one phase to another. Usually the change occurs when adding or removing heat at a particular temperature, known as the melting point or the boiling point of the substance. Removing heat from a substance changes a gas to a liquid or a liquid to a solid.

Common changes of state include melting, freezing, sublimation, deposition, condensation, and vaporization.

I can describe the 6 changes of state (melting, freezing, vaporization, condensation, sublimation, and deposition) in terms of what happens to the energy and spacing of the particles.

A phase change is when matter changes to from one state (solid, liquid, gas, plasma) to another. (see figure 1). These changes occur when sufficient energy is supplied to the system (or a sufficient amount is lost), and also occur when the pressure on the system is changed.

Sublimation, deposition, condensation, evaporation, freezing, and melting represent phase changes of matter.

Phase changes, such as the conversion of liquid water to steam, provide an important example of a system in which there is a large change in internal energy with volume at constant temperature.

1. One way to recognize a phase change is by measuring the temperature of a substance as it is heated or cooled.
2. The temperature of a substance does not change during a phase change. Consider the phase change of Naphthalene, a compound that is sometimes used in mothballs.

The process of a solid becoming a liquid is called melting. (an older term that you may see sometimes is fusion). The opposite process, a liquid becoming a solid, is called solidification. For any pure substance, the temperature at which melting occurs—known as the melting point—is a characteristic of that substance.

Phase changes include vaporization, condensation, melting, freezing, sublimation, and deposition. Evaporation, a type of vaporization, occurs when particles of a liquid reach a high enough energy to leave the surface of the liquid and change into the gas state.

Phase state changes. A change of state is usually accompanied by a change in temperature and/or pressure. Matter commonly exists in one of three forms, or states: solid, liquid, or gas. One fundamental way in which these three states differ from each other is the energy of the particles of which they are made.

Matter undergoes phase changes or phase transitions from one state of matter to another. Below is a complete list of the names of these phase changes. The most commonly known phase changes are those six between solids, liquids, and gasses.However, plasma also is a state of matter, so a complete list requires all eight total phase changes.

Sublimation is the change of state from solid to gas. Some of the solid matters change their states directly to the gas with the gained heat. For example, dry ice (frozen CO2) sublimate when heat is given. Inverse of this process is called deposition, in which gas matters lost heat and change their phase to solid.

Figure 1 also shows phase changes that are rare (on Earth, at least) known as plasma. However, figure 1 does not show what happens when gases or liquids get to sufficiently high pressures and temperatures that they can’t be distinguished.