CHEMISTRY Nov 16, 2009

Warm Up Name the different phase changes of a matter –For example: Solid  Liquid (Melting)

Agenda Unit 4 Phase Changes Notes and Heat Transfer Collect Progress Report Homework –Phase Change Worksheet –Last Day for Make up Work : Wednesday –Research Project: Due Thursday/Friday

Phase Changes Explain how the addition and removal of energy can cause a phase change To learn about interactions among water molecules. To understand and use heat of fusion and heat of vaporization. Interpret a heating/cooling curve for water

Phase Changes Refer to diagram –Six possible transitions between phases

Phase Changes that Require Energy What happens to molecules in a solid as it melts? Melting –The amount of energy (heat of fusion) required to melt one mole of a solid depends on the strength of the forces keeping the particles together (Intermolecular force).

Phase changes that require energy When liquid water is heated, some molecules escape from the liquid and enter the gas phase.

Phase changes that require energy If a substance is usually a liquid at room temperature (as water is), the gas phase is called a vapor. Vaporization is the process by which a liquid changes into a gas or vapor. As temperature increases, water molecules gain kinetic energy –At Boiling point, molecules throughout the liquid have the energy to enter the gas or vapor phase.

Phase changes that require energy The process by which a solid changes directly into a gas without first becoming a liquid is called Sublimation. –Solid air fresheners and dry ice are examples of solids that sublime.

Phase changes that release energy Some phase changes release energy into their surroundings. For example, when a vapor loses energy, it may change into a liquid. Condensation is the process by which a gas or vapor becomes a liquid. It is the reverse of vaporization.

Phase changes that release energy Water vapor undergoes condensation when its molecules lose energy, their velocity decreases. The freezing point is the temperature at which a liquid becomes a crystalline solid. When a substance changes from a gas or vapor directly into a solid without first becoming a liquid, the process is called deposition. –Deposition is the reverse of sublimation. Frost is an example of water deposition.

Phase Change Diagram Potential energy (E p ) –Stored energy Energy of position Chemical energy (gas or food) Electrical energy (batteries) Kinetic energy (E k ) –Motion Mechanical energy Radiant (E d ) –Heat/Light/Sound

Summary: Phase changes (Refer to handout: Label phases, Label energy change, draw atomic diagram at each phase ) Energy or Time Temperature Heating Curve

Practice Substance Freezing point ( o C)Boiling Point ( o C) Water Gallium Iron At room temperature (27 o C), Iron is a solid, mixture, liquid or gas? At 800 o C, Iron is a solid, mixture, liquid or gas? During the process of heating water from 27 to 85 o C : –Did the potential energy change? Kinetic energy? –Is it an endothermic or exothermic reaction?

Homework Phase Change Worksheet

Methods of Heat Transfer online.com/objects/index_tj.asp?objid=SC E304

Methods of Heat Transfer Conduction: –Transfer of heat between substances that are in direct contact with each other Occurs mainly in solid Better conductor  More rapid heat transfer –Examples of good and poor conductors? Convection: –Up and down movement (circulation) of gases and liquids caused by heat transfer Does not occur in solid (molecules not free to move around) Examples of convection? Radiation: –Electromagnetic waves traveling through space Does not require a medium to transfer heat –Waves transfer heat to the object Examples of radiation heat transfer?

Practice Heat Transfer Boiling water over a campfire Melting a tub of ice cream on the kitchen counter Electric Stove versus Gas Stove –Which stove will boil water faster? Why? Why is the second floor usually warmer than the first floor? Why?

Warm Up Energy Conversions –Flash Light A 20 g sample of water is put into a calorimeter and heated until its temperature increases from 60 to 80 o C. If the specific heat of water is 4.184J/g. o C, calculate the heat absorbed by the water.

Conversions Converting between o C & o F –ºC = 5/9(ºF – 32) –ºF = 9/5 (ºC) + 32 Converting between o C & K –ºC = K – 273 –K = ºC Practice Problems –Convert 37 ºC to K –Convert 100 o F to ºC –Convert 50 o F to K

Conversions The breakfast shown in the photograph contains 230 nutritional Calories. How much energy in joules will this healthy breakfast supply? Conversion factor 1 Calorie = 1000 calories 1 cal = 4.19 Joules

Calorimetry Practice Problems What amount of heat would be given off by 3.0 x 10 3 g of water in order to lower its temperature from 95 o C to 12 o C?

Practice Problem If 5603 joules of heat is added to 5.6 g of water at a temperature of 15 o C, what will the final temperature be? What amount of heat would be given off by 7.0 x 10 3 g of water in order to lower its temperature by 5 o C?

Practice Problem What is the specific heat of lead that has a mass of 30 g and undergoes a 250 o C change while absorbing calories? Copper has a specific heat of J/g. o C. What is the mass of a piece of copper that undergoes a 25 o C temperature change when it absorbs 755 J of energy?

Conversions Converting between o C & o F –ºC = 5/9(ºF – 32) –ºF = 9/5 (ºC) + 32 Converting between o C & K –ºC = K – 273 –K = ºC Practice Problems –Convert 37 ºC to K –Convert 100 o F to ºC –Convert 50 o F to K

Conversions The breakfast shown in the photograph contains 230 nutritional Calories. How much energy in joules will this healthy breakfast supply? Conversion factor 1 Calorie = 1000 calories 1 cal = 4.19 Joules

Practice Problems Refer to handout –Specific heat problems

CHEMISTRY September 29, 2010

Warm Up Study for Quiz –5 minutes

Agenda Quiz Homework –Research Project Presentation Due Thursday/Friday –Extra Credit: Dress Up

Quiz 20. Draw what happens to kinetic energy in water as you cool it from 90 o C to 10 o C (Use circles to represent molecules! Use “whoosies” to represent speed of molecules) 21. What does it mean when an energy resource is said to be “renewable”? Provide 2 examples 22. What are “fossil fuels”? Which non- renewable energy resources are “fossil fuels”?