Change Of Phases of Matter
Check us out at http://www.tutorvista.com//videos The term 'change of phase' means the same thing as the term 'change of state'. There are four states, or phases, of matter. They are: •Solid •Liquid •Gas •Plasma We will not be discussing the plasma state here. When a substance changes from one state, or phase, of matter to another we say that it has undergone a change of state, or we say that it has undergone a change of phase. These changes of phase always occur with a change of heat. Heat, which is energy, either comes into the material during a change of phase or heat comes out of the material during this change. However, although the heat content of the material changes, the temperature does not. We will list five changes of phase. They are diagrammed in the above animation and listed below. Description of Phase ChangeTerm for Phase ChangeHeat Movement During Phase ChangeTemperature Change During Phase Change Solid to liquidMeltingHeat goes into the solid as it melts.None Liquid to solidFreezingHeat leaves the liquid as it freezes.None Liquid to gasVaporization, which includes boiling and evaporationHeat goes into the liquid as it vaporizes.None Gas to liquidCondensationHeat leaves the gas as it condenses.None Solid to gasSublimationHeat goes into the solid as it sublimates.None So, how could there be a change in heat during a phase change without a change in temperature? Remember that heat is energy, and remember that there are two types of energy - kinetic and potential. The heat exchanges, or energy exchanges, present during a change in phase are changes in potential energy. These energy exchanges are not changes in kinetic energy. If heat is coming into a substance during a phase change, then this energy is used to break the bonds between the molecules of the substance. The example we will use here is ice melting into water. After the molecular bonds in the ice are broken the molecules are at a higher potential energy state, however they are not on the average moving any faster, so their average kinetic energy remains the same, and thus, their Kelvin temperature remains the same.