Phase Changes

Phase Changes

Standard • PS 3.7 - Explain the process of phase change in terms of temperature, heat transfer, and particle arrangement

Temperature • Temperature - the term used to describe the average kinetic energy of the particles in a substance • Kinetic energy is the type of energy associated with motion • The faster particles are moving at higher temperatures

Phase Change - What does it have to do with The Kinetic Theory? • Phase change is due to changing the movement (energy) of the particles

Freezing/Melting Point • The freezing or melting point is the temperature where a phase change occurs between a liquid and a solid. • If heat is being added at this temperature attractions between particles will break and a solid will melt • If heat is being taken away attractions will form between particles and a liquid will freeze.

Boiling Point • Boiling Point is the temperature where a liquid is changing to a gas throughout the liquid. • Boiling occurs when the bubbles of the vapor are formed

What affect does adding energy have? • When energy is added to a substance, the energy of the particles of the substance increases. • Evidence of this would be that the temperature of the substance increases or a phase changes

What affect does adding energy to a solid have? • When heat is added to a solid the particles move faster and the temperature will increase until the temperature of the solid reaches its melting point • When the temperature of the solid is equal to the melting point and more heat is added the temperature will not change. • The extra heat is used to break the attractions to change from a solid phase to the liquid phase

What affect does adding energy to a liquid have? • When heat is added to a liquid the particles move faster and the temperature will increase until the liquid reaches its boiling point • When the temperature of a liquid is equal to the boiling point and more heat is added to the substance the temperature will not change • The extra heat will be used to break the attraction between the molecules of that liquid and change the phase to a gas. • When a substance boils it forms bubbles of the gas

Temperature vs. Time Graph

Temperature vs. Time Graph • The line of the graph has a positive slope until a phase change occurs • At the melting point or boiling point the temperature does not change as more heat is added over time. The slope of the line will be flat during the time that time phase is changing • After the phase change the slope of the line becomes positive again

Can liquids evaporate at any temperature? • Liquids may evaporate at any temperature • This is because some of the molecules at the surface are moving fast enough to escape the attraction of the other molecules

Can something go from a solid to a gas? • Sublimation is the process where solids change directly to gases • Sublimation may occur in some substances, such as dry ice (solid carbon dioxide) because the melting point and boiling point are almost the same