 What is a system? › The components that are being studied  What are the states of matter?  What is a phase? › A region that has the same composition and properties throughout › Think about a glass of ice water…..how many phases are present in the glass?

 Atmosphere  kPa  mmHg 1 atm = kPa = 760 mmHg

 Equilibrium – the state in which a process and the reverse process occur at the same rate › Phases – involves changes of state › Chemical reactions – involves equal amounts of products and reactants being formed at the same time  Vapor pressure – the partial pressure exerted by a vapor that is in equilibrium with its liquid state

 Boiling point › The temperature at which the vapor pressure equals the external pressure › As the temperature of the water increases, molecules have more kinetic energy, so more enter the gas phase. This causes an increase in vapor pressure.  Melting point › The temperature at which a solid and liquid are in equilibrium › Not affected by changes in pressure

 A graph of the relationship between the physical state of a substance and the temperature and pressure of the substance  Contains 3 lines: › Vapor pressure curve – liquid/gas equilibrium  Changes of state? › Liquid/solid equilibrium  Changes of state? › Solid/gas equilibrium  Changes of state?

 Terms – › Triple point – the point where all three lines meet › Critical point – the temperature and pressure at which the gas and liquid states of a substance become identical and form one phase (called a supercritical fluid)  Phase diagrams are unique to each pure substance and can be used to help identify an unknown substance

 Triple point = -56.7ºC, 518 kPa  Critical point = 31.1ºC, 7.38 x 10 3 kPa  Vapor pressure of the solid at 1 atm = -78.5ºC  Label › X-axis – Temperature › Y-axis – Pressure

 Vapor pressure curve of the solid goes from the triple point through -78.5ºC and 1 atm (101.3 kPa).  Line for equilibrium between solid and liquid begins at the triple point, goes upward almost vertically, and has a slightly positive slope  See graph on p. 403 to compare your graph.

 The horizontal line at 1 atm does not intersect the solid-liquid line  Think about dry ice…..Carbon dioxide is never a liquid at standard pressure  Solid carbon dioxide sublimes at -78.5ºC

 Page 404 – Practice problems