1. CHEMISTRY September 21, 2010

2. Warm Up What is the difference between heat and temperature? Which bench will you sit on when exposed to 120 o F sunlight -- a wood or an iron bench? Why?

3. Agenda Warm Up Grade Unit 3 Worksheet 1 and 2 Answers to Post Test Questions Unit 3 Lecture Homework –Unit 3 Worksheet 3

4. Grade Homework Unit 3 Worksheet 1: Forms of Energy Unit 3 Worksheet 2: Energy Calculations

5. Post-Test Questions (Video) Refer to Packet

6. Chemistry September 22, 2010

7. Warm Up Why is it cold when you hold on to a piece of ice cube? –How is heat transferred?

8. Agenda Warm Up Unit 3: Energy Practice Problems Homework: –Unit 3 Worksheet –Unit 3 Quiz

9. Unit 3 Recap: Energy Part I: Forms of Energy Part II: Measurements of Energy and SI Unit Measured by amount of work it can do - OR- amount of heat it can be changed into SI unit of measure = Joule (J) Part III: Energy Conversions and Energy Efficiency A. Energy is changed, or converted, from one form to another B. Law of Conservation of Energy –The total amount of energy remains the same during all energy changes. –Energy cannot be created or destroyed

10. Thermochemistry

11. Chemical Energy and the Universe Thermochemistry is the study of heat changes that accompany chemical reactions and phase changes. In thermochemistry, the system is the specific part of the universe that contains the reaction or process you wish to study.

12. Chemical Energy and the Universe Everything in the universe other than the system is considered the surroundings. Therefore, the universe is defined as the system plus the surroundings. universe = system + surroundings

13. Enthalpy and enthalpy changes For many reactions, the amount of energy lost or gained can be measured conveniently in a calorimeter at constant pressure. To more easily measure and study the energy changes that accompany such reactions, chemists have defined a property called enthalpy. Enthalpy (H) is the heat content of a system at constant pressure.

14. Complex Calorimeter

15. Simple Calorimeter Test Tube Stirring Rod Thermometer Reaction Water Sealed Container

16. Enthalpy and enthalpy changes You can measure the change in enthalpy, which is the heat absorbed or released in a chemical reaction. –What is the direction of heat flow? The change in enthalpy for a reaction is called the enthalpy (heat) of reaction (∆Hrxn).

17. Enthalpy and enthalpy changes

18. IV. Energy and Chemical Reactions A. Exothermic Reaction –Release heat energy B. Endothermic Reaction –Absorb heat energy C. Activation energy – Minimum amount of energy needed to get a reaction started

19. V. Heat and Temperature A. Celsius Scale –Freezing point of water = 0 o C –Boiling point of water = 100 o Celsius –Interval between them is divided into 100 parts B. Kelvin Scale –Absolute zero Lowest temperature theoretically possible –Absolute zero = 0 K = -273 o C –Size of degree is same as Celsius Fahrenheit Scale

20. C. Converting –Kelvin = Celsius + 273 (K = o C + 273) –Celsius = Kelvin – 273 ( o C = K -273) –Fahrenheit = ( o C × 9/5) + 32 D. Heat –Measured by temperature change it produces in substance –Calorie Quantity of heat that will increase the temperature of 1 gram of water by 1 o C – 1 calorie (cal) = 4.19 Joules (J) E. Heat vs Temperature –Refer to the board

21. Heat versus Temperature Heat –Energy that transfers from one object to another because of a temperature difference between them. Temperature –A measure of the average kinetic energy of the particles in a sample of matter

22. VI. Changes in Temperature When heated, different substances change temperature at different rates. Specific Heat –The amount of heat it takes to raise the temperature of 1 g of substance by 1 o C. Specific heat of water = 1 cal/g. o C Specific heat of Iron = 0.11 cal/g. o C

23. VII. Calorimetry Measurement of the amount of heat released during a reaction Heat measured using a calorimeter (refer to diagram) –Calorimeter = device to measure the transfer of heat to water –To calculate the calories of heat transferred during a chemical reaction, multiply: Mass of substance in calorimeter (g)  m Change in temperature ( o C)  T Specific heat (calorie/g. o C)  c –Formula Refer to the board

24. Simple Calorimeter Test Tube Stirring Rod Thermometer Reaction Water Sealed Container

25. Examples 2000 grams of water has its temperature raised by 3.0 o C. How much heat was produced? How many calories must be added to 5000 g of water to change its temperature from 20 o C to 30 o C? If 500 g of water at 25 o C loses 2500 calories, what will be the final temperature?

26. CHEMISTRY September 23, 2010

27. Warm Up No Warm Up Grade Worksheet

28. Agenda Warm Up Grade Worksheet 1 Complete Unit 3 Notes Unit 3 Quiz: Conversions and Calorimetry Unit 3: Research Project Homework –Research Project –Organize Binder

29. Homework Calorimetry Worksheet 1

30. Energy Measurement Joule

31. Energy Notes Unit: Conversion (c to J) Metric = joule (J) US = calorie (c) –1 calorie is the amount of heat needed to raise 1 g of H 2 O by 1 °C –1000cal = 1Cal = 1 kilocalorie = food Calories 4.184 J = 1 cal

32. Energy Notes Example –A student uses 30 J of energy putting books on the shelf in the classroom. How many calories of energy did the student exert? –A student eats an entire bag of plan popcorn which contains 60.1 Calories. How many Joules of energy is this?

33. Group Quiz Calories and Joules 1.Convert 3.26 calories to joules. 2.How many joules of energy are in a snickers candy bar (320 Calories)? 3.How many calories are in 83.2 kJ? 4.If you ran 6 miles you would burn approximately 3000. kJ, how many Calories is this?

34. VIII. Kinetic Theory A. Matter has small particles in continuous motion B. The faster a particle moves, the greater the kinetic energy C. Temperature –Measure of the average kinetic energy of particles in the sample. At absolute zero, the average kinetic energy is zero Higher temperatures have a greater average kinetic energy Samples at the same temperature have the same average kinetic energy

35. Figure 3.12: Equal masses of hot water and cold water separated by a thin metal wall in an insulated box. Is anything going to happen?

36. Figure 3.13: The H 2 O molecules in hot water have much greater random motions than the H 2 O molecules in cold water.

37. Figure 3.14: The water samples now have the same temperature (50°C) and have the same random motions.

38. Energy Notes Heat Examples Energy transferred from one body to another due to a temperature difference. –Energy stored in the random motion of molecules Sunlight heating the earth Hot plate with beaker of water

39. D. Transfer of heat into or out of a sample –Heat transferred into a sample can be used to increased the average kinetic energy of the particles This causes an increase in temperature When a sample cools, the particles lose kinetic energy. Heat is given off. –Heat can also enter or leave a sample without causing a change in temperature. When ice melts, the heat absorbed is used to rearrange the particles, not to increase the kinetic energy of the particles No change in temperature occurs

40. Energy Notes Exothermic Endothermic System that releases energy into its surroundings Release energy because a change has occurred Combustion reactions System that takes energy in as heat from the surroundings Need energy from outside source in order for a change to occur Phase change – boil water

41. Reaction Spontaneity Entropy (S) is a measure of the disorder or randomness of the particles that make up a system. Spontaneous processes always result in an increase in the entropy of the universe. Several factors affect the change in entropy of a system. –Changes of state –Dissolving of a gas in a solvent –Change in the number of gaseous particles –Dissolving of a solid or liquid to form a solution –Change in temperature

42. Unit 3 Quiz Refer to Handout Make sure you show your work! –No work = No credit!

43. 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?

44. 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?

45. 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 229.5 calories? Copper has a specific heat of 0.387 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?