-Changes of State -Phase Diagrams Honors Chemistry Mrs. Coyle
Liquids Intermolecular attractions hold molecules of liquids together. Incompressible, definite volume. More dense than gases. Molecules have kinetic energy.
Vaporization Change of phase from a liquid to a gas
Evaporation Vaporization occuring at the surface of the liquid.
Evaporation example: Bromine Gas (Vapor) Liquid
What happens to the rate of evaporation as the liquid is heated? The rate of evaporation increases.
Evaporation is a cooling process Why? The particles with the higher kinetic energy escape the liquid first.
Boiling Evaporation occurring beneath the liquid’s surface.
Evaporation in a Closed Container
Evaporation in a Closed Container Liquid Vapor When the rate of evaporation equals the rate of condensation the system is in equilibrium.
Le Chatelier’s Principle (Henri Le Chatelier, 1884) If a stress is applied to a system in equilibrium, the system will tend to act so as to reduce the stress. Ex: If you place a hot penny in a container that has H2O (l) and H2O (s) at equilibrium, the system, the heat from the penny will be absorbed and there will be more liquid H2O than before.
Vapor Pressure The pressure of the gas that has evaporated above a liquid.
The vapor pressure increases with increasing temperature. Why? Because the kinetic energy of the liquid molecules increases and more leave the liquid and collide with the walls of the container.
Boiling Point The temperature at which a liquid boils.
Boiling and External Pressure When the external pressure is greater than the vapor pressure of the bubbles in the liquid the bubbles cannot come to the surface. Boiling does not happen.
Boiling and External Pressure When the external pressure is equal to the vapor pressure of the bubbles in the liquid, boiling occurs.
Why does water boil at a lower temperature at high altitudes? Because the external pressure is lower.
Normal Boiling Point The boiling point at 1 atm or 101.3kPa
Phase Diagram for Water A Triple Point C Critical Temperature