Weather Unit – Investigation II Lesson 4: It’s Only a Phase

© 2004 Key Curriculum Press. Unit 3 Investigation II Admit Slip Suppose you put a pot of water on the stove on “high” (about 350°F or 170  C). After the water boils for about ten minutes, the temperature of the water is 212°F. What is happening to the water? Why is the temperature of the water 212°F and not 350°F like the stove?

© 2004 Key Curriculum Press. Unit 3 Investigation II The Big Question What happens to the temperature of water as it is heated?

© 2004 Key Curriculum Press. Unit 3 Investigation II Today’s Objectives: Students will be able to: Describe what happens to water as it is heated and cooled. Identify the names of different phase changes Convert Temperature in Celsius to Fahrenheit and Kelvin Agenda: Admit Slip, Homework Review, Notes, Classwork, Exit Slip

© 2004 Key Curriculum Press. Unit 3 Investigation II Heat is the transfer of energy between two objects due to temperature differences. Temperature is the measurement of the average kinetic energy of atoms and molecules. When temperature rises, the atoms and molecules have more energy and move around more. Heat, Temperature, and Phase Changes 5/29/14

© 2004 Key Curriculum Press. Unit 3 Investigation II The relationship between temperature in degrees Celsius  C and degrees Fahrenheit  F is:  F = 9/5 (  C) + 32 or  F = 1.8 (  C) + 32 Another temperature measurement used in science is called Kelvin.K= °C Absolute zero is the temperature at which the volume of a gas and its amount of movement equal 0. Absolute zero is 0 K and is equal to –273 ˚C.

© 2004 Key Curriculum Press. Unit 3 Investigation II Do a Quick Sketch (cont.)

© 2004 Key Curriculum Press. Phases and movement. Solid phase: Particles are in a fixed position but they can vibrate. Liquid phase: Particles are loosely connected but they can flow. A liquid will conform to a container. Gas phase: Particles are free to move and bounce around a room. Gases will expand to fill a container. Unit 3 Investigation II

© 2004 Key Curriculum Press. Unit 3 Investigation II Phase Diagram

© 2004 Key Curriculum Press. Unit 3 Investigation II SUBLIMATION SOLIDIFICATION MELTING FREEZING BOILING / EVAPORATION CONDENSATION SOLID LIQUID GAS Please label all the arrows

© 2004 Key Curriculum Press. Unit 3 Investigation II Fixed temperatures for a given substance: Melting/ Freezing point is a fixed temperature where solid and liquid coexist Boiling point is a fixed temperature where liquid and gas coexist Sublimation / Solidification point is a fixed temperature where solid and gas coexist (cont.)

© 2004 Key Curriculum Press. Only pure water boils at 100 °C and freezes at 0 °C. If there are impurities or additives to the water, the temperatures for freezing and boiling change It takes more energy to boil water with impurities, so impure water will boil at a higher temperature. This is called boiling point elevation. Unit 3 Investigation II

© 2004 Key Curriculum Press. Unit 3 Investigation II You need to remove more energy to freeze water with impurities, so impure water needs to reach a colder temperature to freeze. This is called freezing point depression. During a phase change, the temperature does not change. The energy is being put into converting the substance from one phase to another and is not used to heat.

© 2004 Key Curriculum Press. Unit 3 Investigation II Exit Slip If you heat a glass of ice water will its temperature automatically go up? When will its temperature increase? Explain.

© 2004 Key Curriculum Press. Unit 3 Investigation II Wrap-Up When ice is in the process of melting (changing phase) the temperature remains at 0°C. When water is in the process of boiling (changing phase), the temperature remains constant at 100°C. If only one phase of a substance is present in a system that is being heated, the temperature of that substance increases. (cont.)

© 2004 Key Curriculum Press. Unit 3 Investigation II Temperature is a measure of the kinetic energy of the molecules of a substance. Heat is a process of energy transfer, the direction of which is determined by temperature. (cont.)