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Phase Equilibrium Reading, Interpreting, and Drawing Phase Diagrams Review: Energy and Phase Changes Two-Phase Systems • A system is a set of components that are being studied. • In this system, are phases, or parts of matter that are uniform. • A lava lamp has two phases (components) • The layers in a lava lamp stay apart because their chemical compositions are different • What makes the two phases of ice water different from each other? Equilibrium • Equilibrium involves constant interchange of particles. • If you open rubbing alcohol, you can smell it. This is because the alcohol diffuses out in the ________________ form. • After you recap the alcohol, an equilibrium is quickly reached again. • A dynamic EQUILIBRIUM is reached when particles are entering the gaseous phase at an equal rate as the particles go back to the liquid phase. • At 0°C, water is freezing at the same rate as the ice is melting. Vapor Pressure and Temp • In a closed container with a sample of liquid in the bottom, there are gaseous particles striking all sides of the container. • These particles are also striking the liquid component. • The pressure exerted by the molecules of a gas, or vapor, phase in equilibrium with a liquid is called the vapor pressure. • As the temp increases, the molecules move ____________, giving them more kinetic energy. This allows more particles to break out of the liquid phase and enter the gas above. • As temp increases, vapor pressure ___________________. Phase Diagrams • The substance’s state depends on the temperature and pressure. • A phase diagram is a graph of the relationship between the physical state of a substance and the temperature and pressure of the substance. • A phase diagrams has three lines. • One line is a vapor pressure curve for the liquid-gas equilibrium. • The second line is for the liquid-solid equilibrium. • And the third is for the solid-gas equilibrium. • The temp and pressure conditions at which the solid, liquid, and gaseous phases of a system coexist at equilibrium is known as the triple point. Phase Diagrams • The x-axis shows temperature • The y-axis shows pressure. • For any given point (x,y) [T, P] you can tell if the substance will be a solid, liquid, or gas. • An area above the gas phase lies the critical point • The critical point is the temperature and pressure at which the gas and liquid states of a substance become identical and form one phase. Water, H2O Phase Diagrams • The lines in between the phases represent the phase equilibrium • i.e. the line between the solid and liquid represents the Solid-Liquid Equilibrium • The Solid-Liquid Equilibrium is nearly vertical.. Why?? • Phase diagrams are unique to a particular substance. • The general structure will be roughly the same, but each substance will have its own BP and MP (Temp and Press) Carbon Dioxide, CO2 Effects of Pressure • Remember, solids and liquids are nearly incompressible. • Most substances, such as carbon dioxide, experience a slight increase in melting point when the pressure increases. • However, the effect of pressure on boiling point is MUCH greater… Why?? Drawing a Phase Diagram • The triple point of sulfur dioxide is at -73°C and 0.17 kPa. The critical point is at 158°C and 7.87x103kPa. The normal boiling point of sulfur dioxide is -10°C. Solid sulfur dioxide is denser than liquid sulfur dioxide. Sketch the phase diagram of sulfur dioxide. • What state is sulfur dioxide in at 200 kPa and -100°C? • What state is sulfur dioxide in at 1 kPa and 80°C? • What happens as you increase the pressure on a sample of sulfur dioxide at -11°C from 150 kPa to 300kPa? More Practice • The triple point of benzene is at 5.5°C and 4.8 kPa. The critical point is at 289°C and 4.29 x 103 kPa. Vapor pressure above solid benzene is 101.3 kPa at 80.1°C. Solid benzene is denser than liquid benzene. Sketch the phase diagram of benzene.