Phase Changes Phase Diagrams and Heating Curves
Phase Diagrams Show the phases of a substance at different temps and pressures. Courtesy Christy Johannesson
Triple Point Plot LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World, 1996, page 488 solid liquid gas melting freezing sublimation deposition vaporization condensation Temperature ( o C) Pressure (atm)
Liquid VaporSolid Normal melting point Normal boiling point Temperature ( o C) Pressure (KPa) Triple point Critical pressure Critical point Critical temperature ,058
Critical Point Critical point: the temperature (called critical temperature) above which a substance will always be as gas regardless of the pressure
Triple Point Pressure and temperature where all three phases of matter exist AT THE SAME TIME!! LRqpJN9zeA LRqpJN9zeA
Law of Conservation of Energy E after = E before 2 H 2 + O 2 2 H 2 O + energy Energy Changes + + WOOF!
Law of Conservation of Energy ENERGY CO 2 + H 2 OC 2 H 2 + O 2 PE reactants PE products KE stopper heat, light, sound E after = E before 2 H 2 + O 2 2 H 2 O + energy Energy Changes + + WOOF!
Law of Conservation of Energy ENERGY C 2 H 2 + O 2 PE reactants PE products KE stopper heat, light, sound E after = E before Energy Changes 2C 2 H 2 + 5O 2 4 CO 2 + 2H 2 O + energy
Heating Curves Temperature ( o C) Time Melting - PE Solid - KE Liquid - KE Boiling - PE Gas - KE
Heating Curves Temperature Change change in KE (molecular motion) depends on heat capacity Heat Capacity energy required to raise the temp of 1 gram of a substance by 1°C Water has a very high heat capacity Courtesy Christy Johannesson
Heating Curves Phase Change change in PE (molecular arrangement) temp remains constant Heat of Fusion ( H fus ) energy required to melt 1 gram of a substance at its m.p. Courtesy Christy Johannesson
Heating Curves Heat of Vaporization ( H vap ) energy required to boil 1 gram of a substance at its b.p. usually larger than H fus …why? EX: sweating, steam burns, the drinking bird Courtesy Christy Johannesson