Tuesday, Dec. 3 rd : “A” Day Wednesday, Dec. 4 th : “B” Day (early out) Agenda  Homework Questions/collect (pg. 398: 1-3, 6-9)  Sec quiz: “Energy of State Changes”  Section 11.4: “Phase Equilibrium” Phase, equilibrium, vapor pressure, phase diagram, triple point, critical point  Homework: Pg 405: #1-5 Concept Review: “Phase Equilibrium” “What Would Life be Like?” paper

Homework pg. 398: #1-3, 6-9  Questions?  Problems?

Section 11.3 Quiz “Energy of State Changes”  You may use your notes, your book, and your lab partner to complete the quiz…

Two-Phase Systems  System: a set of components that are being studied.  Phase: a part of matter that is uniform (a region that has the same composition and properties throughout) For example, ice water is a system that has a solid phase and a liquid phase.

Equilibrium Involves Constant Interchange of Particles  Equilibrium: the state in which a chemical process and the reverse chemical process occur at the same rate such that the concentrations of reactants and products do not change.  A dynamic equilibrium exists when particles are constantly moving between two or more phases yet no net change in the amount of substance in either phase takes place.

Example  If you open a bottle of rubbing alcohol, you can smell the alcohol.  When you put the cap back on, an equilibrium between the liquid phase and the gas phase is quickly reached.  That is, the rate of evaporation equals the rate of condensation.

Vapor Pressure Increases with Temperature  For an enclosed gas and liquid in equilibrium,like the rubbing alcohol, the gas particles above the liquid exert pressure when they strike the walls of the container.  Vapor pressure: the partial pressure exerted by a vapor that is in equilibrium with its liquid state at a given temperature.  The boiling point is the temperature at which the vapor pressure equals the external pressure.

Vapor Pressure Increases with Temperature  As you increase the temperature of a closed system, more liquid particles escape into the gas phase.  Thus, as you increase temperature, the vapor pressure of the substance also increases.  When you increase the temperature of a system to the point at which the vapor pressure of a substance is equal to standard atmospheric pressure have reached the substance’s normal boiling point.

Vapor Pressure Increases with Temperature  The dotted line represents atmospheric pressure and shows the normal boiling point.

Phase Diagrams  A substance’s phase depends on temperature and pressure.  To get a complete picture of how temperature and pressure are related for a particular substance, you can look at a phase diagram.  Phase diagram: a graph that shows the relationship between the physical state of a substance and the temperature and pressure of the substance.

Phase Diagrams  A phase diagram has three lines: One line shows the liquid-gas equilibrium. Another line shows the liquid-solid equilibrium A third line shows the solid-gas equilibrium.  These three lines meet at the triple point.  Triple point: the temperature and pressure conditions at which the solid, liquid and gaseous phases of a substance coexist at equilibrium.

Phase Diagram for Water

Phase Diagrams Relate State, Temperature, and Pressure  For any given point (x, y) on a phase diagram, you can determine what the state of a substance will be.

Gas-Liquid Equilibrium for Water  Line AD shows liquid-vapor equilibrium.  As you follow line AD upwards, the vapor pressure is increasing, so the density of the vapor increases and the density of the liquid decreases.  Critical point: the temperature and pressure at which the gas and liquid states of a substance become identical and form one phase.  Above this point, the substance is called a supercritical fluid.

Solid-Liquid Equilibrium for Water  Line AC shows solid-liquid equilibrium.  Only solid is present to the left of line AC.  Water is an unusual substance: the solid is less dense than the liquid. Why? Hydrogen bonding!  The line AC has a slightly negative slope, which is very rare in phase diagrams of other substances.

Solid-Gas Equilibrium for Water  Line AB shows solid-vapor equilibrium.  If the pressure is decreased below the line AB, the solid will sublime.  Freeze-drying uses the process of sublimation of ice below the freezing point to dry foods.

Phase Diagrams Are Unique to a Particular Substance  Each pure substance has a unique phase diagram, although the general structure is the same.  The triple point is characteristic for each substance and serves to distinguish the substance from other substances.  Unlike boiling point, the melting point is affected little by changes in pressure, so the solid-liquid equilibrium line is nearly vertical in phase diagrams.

Phase Diagram for CO 2

 Notice that in the phase diagram for carbon dioxide, the horizontal line at kPa does not intersect the solid-liquid line.  That’s because carbon dioxide is never a liquid at standard pressure.  At room temperature, solid carbon dioxide sublimes, or changes directly from a solid to a gas.

Homework  Section 11.4 Review, Pg. 405: #1-5  Concept Review: “Phase Equilibrium”  “What Would Life Be Like?” Paper Due Mon/Tues *Lab next time* Chapter 11 Test/Concept Review Due: Friday, 12-13: “A” Day Monday, 12-16: “B” Day