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Section 12.4 Phase Changes • Explain how the addition and removal of energy can cause a phase change. • Interpret a phase diagram. phase change: a change from one state of matter to another Section 12.4 Phase Changes (cont.) melting point freezing point vaporization condensation evaporation deposition vapor pressure phase diagram boiling point triple point Matter changes phase when energy is added or removed. 12.4 Phase Changes That Require Energy http://www.youtube.com/watch?v=2E4uK6zoJmo •Watch the video and copy his diagram (see Colson’s white board) p. 425 Phase Changes That Require Energy (cont.) • The melting point of a crystalline solid is the temperature at which the forces holding the crystal lattice together are broken and it becomes a liquid. • Molecules are freer to move as solid liquid gas Phase Changes That Require Energy (cont.) p. 426 Once over the hump of KE, substance can vaporize Phase Changes That Require Energy (cont.) • Vaporization is the process by which a liquid changes to a gas or vapor. • Evaporation is vaporization only at the surface of a liquid. Phase Changes That Require Energy (cont.) • In a closed container, the pressure exerted by a vapor over a liquid is called vapor pressure. •In closed container, water leaving/ entering is equal Phase Changes That Require Energy (cont.) • The boiling point is the temperature at which the vapor pressure of a liquid equals the atmospheric pressure. Phase Changes That Require Energy (cont.) • Sublimation is the process by which a solid changes into a gas without becoming a liquid. Phase Changes That Release Energy • As heat flows from water to the surroundings, the particles lose energy. • The freezing point is the temperature at which a liquid is converted into a crystalline solid. • FYI: Melting point and freezing point are the same points, just opposite direction of phase change Phase Changes That Release Energy (cont.) • As energy flows from water vapor, the velocity decreases. •Deposition is the process by which a gas or vapor changes directly to a solid, and is the reverse of sublimation. • The process by which a gas or vapor becomes a liquid is called condensation. Phase Diagrams • A phase diagram: • graph of pressure versus temperature • shows in which phase a substance will exist under different conditions of pressure and temperature. Phase Diagrams (cont.) • The triple point is the point on a phase diagram that represents the temperature and pressure at which all three phases of a substance can coexist. p. 429 What do the Lines of a Phase Diagram tell me? 1. Short Yellow Curve: Shows T & P conditions under which solid water & water vapor can co-exist. 2. Long Blue Curve: shows T & P conditions under which liquid water & water vapor can co-exist 3. Red Curve: shows the T & P conditions under which solid water & liquid water can co-exist What do the Lines of a Phase Diagram tell me? A. Triple Point: defined on earlier slide B. Critical Point: this point indicates the critical T & P above which water cannot exist as a liquid Phase Diagrams (cont.) • The phase diagram for different substances are different from water. p. 430 Bright Storm Video •http://www.youtube.com/watch?v=e1mo-BVIvcA Section 12.4 Assessment The addition of energy to water molecules will cause them to ____. A. freeze B. change to water vapor D A 0% C D. move closer together A. A B. B C. C 0% 0% 0% D. D B C. form a crystal lattice Section 12.4 Assessment The transfer of energy from one object to another at a lower temperature is ____. A. heat B. degrees D A 0% C D. electricity A. A B. B C. C 0% 0% 0% D. D B C. conductivity Energy and Chemical Change Section 15.1 Energy Section 15.2 Heat Section 15.3 Thermochemical Equations Section 15.4 Calculating Enthalpy Change Section 15.5 Reaction Spontaneity Click a hyperlink or folder tab to view the corresponding slides. Exit Section 15.1 Energy • Define energy. • Distinguish between potential and kinetic energy. • Relate chemical potential energy to the heat lost or gained in chemical reactions. • Calculate the amount of heat absorbed or released by a substance as its temperature changes. temperature: a measure of the average kinetic energy of the particles in a sample of matter Section 15.1 Energy (cont.) energy law of conservation of energy chemical potential energy heat calorie joule specific heat Energy can change form and flow, but it is always conserved. The Nature of Energy • Energy is the ability to do work or produce heat. • Two forms of energy exist, potential and kinetic. • Potential energy is due to composition or position. • Kinetic energy is energy of motion. The Nature of Energy (cont.) • The law of conservation of energy states that in any chemical reaction or physical process, energy can be converted from one form to another, but it is neither created nor destroyed—also known as the first law of thermodynamics. The Nature of Energy (cont.) • Chemical potential energy is energy stored in a substance because of its composition. • Chemical potential energy is important in chemical reactions. • Heat is energy that is in the process of flowing from a warmer object to a cooler object. • q is used to symbolize heat/energy. Measuring Heat • A calorie is defined as the amount of energy required to raise the temperature of one gram of water one degree Celsius. • Food is measured in Calories, or 1000 calories (kilocalorie). • A joule is the SI unit of heat and energy, equivalent to 0.2390 calories. Measuring Heat (cont.) Specific Heat • The specific heat of any substance is the amount of heat required to raise one gram of that substance one degree Celsius. • Some objects require more heat than others to raise their temperature. Specific Heat (cont.) • Calculating heat absorbed and released • q = c × m × ∆T • q = heat absorbed or released • c = specific heat of substance (see Table 15.2) • m = mass of substance in grams • ∆T = change in temperature in Celsius Click here for tutorial video Section 15.1 Assessment The heat required to raise one gram of a substance by one degree Celsius is called ____. A. joule A 0% D D. energy C C. specific heat A. A B. B C. C 0% 0% 0% D. D B B. calorie Section 15.1 Assessment Which of the following is an example of chemical potential energy? A. the moon orbiting Earth B. a car battery D A 0% C D. a roller coaster at the top of a hill A. A B. B C. C 0% 0% 0% D. D B C. a compressed spring