Fire!

1. Fire!

2. Chem CatalystFired Up Today you will be observing several different combustion reactions. 1.) What do you think a combustion reaction is? 2.) There are 3 general things needed for a combustion reaction to occur – what are they?

3. Fire Safety • Tie back long hair, which is especially flammable when mixed with hair spray. Avoid loose clothing. • Small fires may be extinguished by smothering flames with water, sand, or a fire blanket. A carbon dioxide fire extinguisher can be used to combat most fires, except fires caused by metals.

4. The Big Question • What are the characteristics of fire?

5. Making Sense • Changes in matter involve changes in energy. • Exothermic process: A process that releases energy in the form of heat. • Reactions of elements and compounds with oxygen typically are exothermic. • Combustion requires oxygen.

6. Predict-Explain-Observe-Explain • A strip of paper is dipped into a mixture of isopropyl alcohol (C3H8O) and water. • Predict what will happen to the paper when it is lit on fire. Explain why you said what you said. • Observe the demonstration. • Explain what happened.

7. Chem CatalystNot So Hot • How do you think hand warmers work? Where does the heat come from?

8. Lab introduction • You will be observing three chemical processes today. Focus on the heat transfer in each one. • Work in groups of four. • Follow directions at the three stations.

9. Preliminary Definition of Energy • Energy: A measure of the work involved in moving or changing something. Ex: changes in temperature • Energy is not a substance (i.e. energy is NOT matter)

10. Definition of Heat • Heat: A transfer of energy between two substances due to temperature differences. • To look at heat, we have to define the system and surroundings.

11. System and Surroundings • System: The process you are focusing on. In this case, a chemical reaction. • Surroundings: Everything outside the system (thermometer, beaker, your body)

12. Definitions • Exothermic: • Feels warm • Gives off heat • Heat transfers from the reaction  your hand • Endothermic Reaction: • Feels cold • Absorbs heat • Heat transfers from your hand  the reaction

13. Computer Simulation • Molecular workbench: search “exothermic”, explosion. • What is happening during an explosion? How is energy transferred?

14. Chem Catalyst • Imagine you are sitting near a campfire. You feel warm. • Explain how you think burning wood transfers heat to your body. • The next morning you find ashes that are the same temperature as the air. Explain why the ashes are no longer hot.

15. ChemCatalyst • You have water at 25ºC. You dissolve ammonium acetate, NH4C2H3O2, in the water and find that the temperature decreases to 17ºC. 1.) Is the process exothermic or endothermic? 2.) How will it feel if you put your hand on it? 3.) In which direction is the heat transferring?

16. Purpose • Today’s question: How do we consider energy transfer from different points of view?

17. Making Sense

18. Instructions for the water stations

19. Making Sense • Was the lukewarm water at the water station hot or cold? • Why did the lukewarm water feel hot to one hand and cold to the other? • If you say something is “hot, what do you mean? • If you say something is “cold,” what do you mean?

20. “Hot” and “Cold” • For the rest of the Fire unit, we won’t say anything is “hot” or “cold.” • Instead, we can say…

21. Definitions • Heat (thermal energy) always transfers from the warmer object to the colder object. • Thermal equilibrium: when two objects in contact with each other reach the same temperature.

22. Laws of Thermo • First Law of Thermodynamics: Energy is conserved. (we can transfer energy, but you can’t create or destroy it) • Second Law of Thermo: Energy tends to disperse - energy flows from objects of high temperatures to low temps.

23. Check-In • Imagine that a thermometer is placed in a beaker of water and the temperature is noted. An ice cube is dropped into the water, and after ten minutes the temperature is noted again. • What will you observe? • What is the direction of energy transfer?

24. Chem Catalyst • You are standing outside freezing with no gloves on for several minutes. You sneeze and get stuff all over your hands. When you come into the house, you turn on the cold faucet and start washing your hands. Why do your hands feel so hot under the water? Draw a picture of the direction of heat transfer.

25. Exercise • Write two sentences, using proper English, that use the word “heat”. • After you are done, identify the part of speech that you use “heat” as for both of your sentences.

26. ChemCatalyst • A thermometer is placed in a beaker of water and the temperature is 21ºC. An ice cube is dropped into the water and after 10 minutes the temperature is 14ºC. • Is this an endo or exothermic process? • What is the change in temperature? • Draw a picture showing the direction of heat transfer.

27. Chem CatalystHeat versus Temperature • Chemists talk about the “average kinetic energy” of molecules very often. What do you think this means? • What chemistry tool could you use to measure the “average kinetic energy” of molecules?

28. Chem CatalystHeat versus Temperature • A lead atom is moving at 40 mph. A hydrogen atom is also moving at 40 mph. Will they have the same temperature or different? Why?

29. Go to computer lab for Heat vs. Temp simulation • Priority #1 = Finishing this assignment • When you are finished, you can work on anything else that is appropriate.

30. Chem CatalystHeat versus Temperature • Write “1/2 day open note quiz” for your chem catalyst • Take out any papers you want to use for the optional NeilMed quiz • I will take whichever grade is higher – either your NeilMed project or the quiz

31. Recall: • Thermal equilibrium is reached when two objects in contact with one another reach the same temperature.

32. Online Simulation • http://jersey.uoregon.edu/vlab/Thermodynamics/index.html • Experiments #1 and #5

33. Questions about the simulation • What happens when you heat the gas atoms in the simulation? • Are all the atoms moving at the same speed? • What happens to the sample when you add atoms? • How can you make the heat energy of the sample increase without increasing the temperature of the sample?

34. Heat vs. Temperature Lab

35. Making Sense

36. Key Points • The final temperature of a mixture depends on mass and temperature of the samples. • Are heat and temperature the same?

37. Definition • Thermal Energy - The total kinetic energy associated with the mass and motions of the particles in a sample of matter.

38. Definition • Calorie: The amount of energy it takes to raise the temperature of one gram of water by one degree Celsius. • The equation for heat transfer in water is:

39. Sample problem • How much heat transfer is required to raise the temperature of 5.0 g of water from 25ºC to 75ºC?

40. ChemCatalyst • GET A CALCULATOR PLEASE • You have one beaker containing 500 g of water at 75ºC. You also have a beaker with 2000 g of water at the same temperature. 1.) Which will melt more ice? Explain your answer in terms of thermal energy, heat transfer, and temperature.

41. Discussion • Does total energy depend on the amount of a substance? • Does the temperature depend on the amount of a substance? • What factors determine how much energy can be transferred from one object to another?

42. ChemCatalyst 1.) Come up to the front of the room and record the temp of both black objects. 2.) Touch both objects. Which do you think will melt an ice cube faster? Why? 3.) Observe what happens when an ice cube is placed on each.

43. Chem Catalyst • Imagine you are at the beach. The sun has been shining all day long, and you want to go for a swim. • How does the sand feel on your feet? How will the water feel? • You go back out to the beach at night for a swim. How does the sand feel now? What about the water?

44. Chem Catalyst • Rank the following substances from coldest to warmest in terms of how they will feel when you touch them. Wood Metal Rubber Stopper Candle Rock Plastic pipe Explain your predictions, please. 

45. Items from Lab Which substances felt coldest? Wood = 0.6 cal/g*ºC Metal = 0.092 cal/g*ºC Rubber Stopper = 0.48 cal/g*ºC Candle = 0.7 cal/g*ºC PVC = 0.215 cal/g*ºC Rock = 0.19 cal/g*ºC

46. Notes Specific Heat Capacity (C): The amount of energy (in calories) needed to raise the temperature of 1 gram of a substance by 1 degree Celsius Different materials have different heat capacities Specific heat capacity for water: 1.00 cal g * ºC In other words, it takes ____ calories to raise ___ grams of water by ____ degrees Celsius

47. Notes Substances with Low Heat Capacity • Transfer heat energy easily (good heat conductor) • Heat up quickly • Cool down quickly Ex: Metals, rocks Substances with High Heat Capacity • DO NOT transfer heat easily • Heat up slowly • Cool down slowly Ex: Wood, Water

48. Class Demonstration How can you explain why the ice cube melted faster on the black metal square? Use what you know about energy transfer and heat capacity.

49. Class Demonstration Feel both black substances. If an ice cube is placed on each substance, which will make it melt faster?

50. ChemCatalyst You have two unknown substances. They each have a temperature of 65 degrees F. The first substances has a heat capacity of 0.12 cal/g*C. The second substance has a heat capacity of 0.63 cal/g*C. Which substance will melt ice faster and WHY?