1. Regents Chemistry Chapter 17 Thermochemistry

2. 2 What is Thermochemistry? Study of heat absorbed and released during chemical reactions. Most of what we learn about thermochemistry in this class will be done later in the year. Right now I will introduce a small amount of material that will help you better understand the reactions we will study during the year.

3. Section 17.1 The Flow of Energy – Heat and Work OBJECTIVES: –Explain how energy, heat, and work are related. –Classify processes as either exothermic or endothermic. –Identify the units used to measure heat transfer. –Distinguish between heat capacity and specific heat.

4. Quantities Used in Thermochemistry Energy - capacity to do work or supply heat –Work – a quantity that describes a force used to change the position and/ or motion of matter Heat the form of energy that is transfer from a body of higher temperature to a body of lower temperature –We use the variable “q” to represent heat –flows from warmer  cooler object –http://www.youtube.com/watch?v=KTHiIwxcexI&feature=r elated (2:45 minutes)http://www.youtube.com/watch?v=KTHiIwxcexI&feature=r elated

5. Forms of Energy Thermal energy is the energy associated with the random motion of atoms and molecules Light energy is the energy associated with electromagnetic radiation (visible, ultraviolet, infared, x- rays, etc.) Nuclear energy is the energy stored within the nucleus of the atom (released with changes in mass of the nucleus) Electrical energy is the energy associated with the flow of electrons Chemical energy – energy associated with chemical change involved in the making or breaking of bonds (ex. Gasoline)

6. 6 Energy These forms of energy can be classified as: Kinetic energy – energy of motion Potential energy – stored energy –In the past you may have looked at the potential and kinetic energy with respect to moving objects. More gravitational potential  energy at top of hill. Due to its position, boulder has potential to do work Less gravitational potential at bottom. Due to its position, boulder has less potential to do work. 

7. 7 The Kinetic Theory of Heat and Temperature Every piece of matter consists of very small particles –These particles of matter are in continuous motion –The faster these particles move the greater the kinetic energy The temperature of a body of matter is actually a measure of the average kinetic energy of the random motions of its particles At absolute zero – particles are no longer in motion

8. 8 The Kinetic Theory of Heat and Temperature The relationship between an object’s temperature and the average kinetic energy of its particles is the same for all kinds of matter –For all bodies at the same temperature, the average kinetic energy of their particles is equal.

9. 9 The Kinetic Theory of Heat and Temperature This theory explains the relationship between heat and temperature –Heat is a form of energy –When heat enters a body, the energy can increase the kinetic energy of the particles of the body, therefore its temperature will increase –When a body cools, its particles lose kinetic energy, and this energy can be given off as heat

10. 10 Conservation of Energy The Law of Conservation of Energy states that in any chemical or physical process, energy is neither created not destroyed –All the energy is accounted for as work, stored energy, or heat When we study heat changes, we consider: –The system – the part of the universe that is the focus of our study –The surroundings – includes everything else in the universe

11. Conservation of Energy Example: When you jump into a pool, your body cools down. Heat is transferred from your body to the water. –System: Your body –Surroundings: everything outside your body (including pool water) –When heat leaves your body it is not lost, it is just transferred

12. Chemical Energy Essentially all chemical reactions, and changes in physical state, involve either: a)release of energy, or b)absorption of energy http://www.youtube.com/watch?v=6n0AtC2Whgshttp://www.youtube.com/watch?v=6n0AtC2Whgs (3:28 minutes) Do you remember this reaction from Biology?

13. Reactions that Release Energy Most reactions release energy as heat These reactions are Exothermic The system loses heat The surroundings heat up Bond making is exothermic

14. 14 ** Gummy Bear Sacrifice ** Gummy Bear Song: (24 sec) http://www.youtube.com/watch?v=1zWykQ8Xc6w&feature=relatedhttp://www.youtube.com/watch?v=1zWykQ8Xc6w&feature=related (2:44 min) http://www.youtube.com/watch?v=Z2kLJp6aeIc&feature=fvwhttp://www.youtube.com/watch?v=Z2kLJp6aeIc&feature=fvw (57 sec)http://www.youtube.com/watch?v=6sAOs6lneug&feature=relatedhttp://www.youtube.com/watch?v=6sAOs6lneug&feature=related (1:44 min) http://www.youtube.com/watch?v=KLtrpGxFPuEhttp://www.youtube.com/watch?v=KLtrpGxFPuE

15. 15 Conclusion question KClO 3 + C 6 H 12 O 6  KCl + O 2 + CO 2 In our experiment, the sugar in the candy released a large amount of energy. Why is it significant to humans that this is an exothermic reaction. What if the reaction was one that absorbed heat or energy?

16. 16 Reactions that Release Energy Activation Energy –Even though a reaction is exothermic, it may still require an initial input of energy to get started This minimum amount of starting energy is called activation energy

17. 17 Reactions that Release Energy the amount of heat released due to bond making is greater than the amount of heat used to start the reaction The solution surrounding the reacting molecules INCREASES in temperature

18. Reactions that Absorb Energy Some reactions absorb heat These reactions are Endothermic system gains heat the surroundings COOL down Bond breaking is endothermic

19. 19 Reactions that Absorb Energy the amount of heat absorbed due to bond breaking is greater than the amount of heat released The solution surrounding the reacting molecules COOLS in temperature

20. 20 Remember? A beaker contains molecules that are reacting. The molecules are in solution. When the reaction: releases heat it is exothermic absorbs heat it is endothermic The solution’s temperature (or surroundings): Increases, warms up Decreases, cools down

21. Measuring & Calculating Heat Flow In order to measure and/or determine the amount of heat lost or gained by a system, we must know: The mass of the system (m) The change in temperature (  T) The specific heat capacity (C) What is specific heat?

22. Specific Heat Capacity Specific Heat Capacity - (“C”) the amount of heat it takes to raise the temperature of 1 gram of the substance by 1 o C A substance’s specific heat depends on both the object’s mass and its chemical composition Water has a HUGE specific heat, when it is compared to other chemicals

23. Specific Heat Capacity For water as a liquid, C = 4.18 J/(g o C) (see Reference Table B) This means that is takes a lot of energy to increase the temperature of water: –And so it takes a long time to heat up Also, water must lose a lot of energy in order to decrease its temperature: –And so it takes a long time to cool off! Water is a great coolant!

24. Measuring & Calculating Heat Flow Remember that reactions absorb or release ENERGY in the form of heat You are all familiar with food “calories” A calorie is a measure of the “energy or heat” of a substance. The calorie unit is defined as the quantity of heat needed to raise the temp of 1 g of pure water 1 o C. a dietary or food Calorie is actually equal to 1 kilocalorie or 1000 cal. “10 grams of sugar has 41 Calories means that 10 grams of sugar releases 41 kilocalories of heat when completed burned”

25. Measuring & Calculating Heat Flow But remember our SI unit for energy is the Joule. 4.184 J = 1 cal 1000 J = 1 kiloJoule or 1kJ

26. Calculating Heat To calculate Heat (q), use the formula: q = mass x C x  T (See Reference Table T) Heat is abbreviated as “q” [Joules] Mass is ALWAYS in grams  T = change in temperature [ o C] C = Specific Heat Capacity J/(g o C) Em Cee Delta T (2:22 min) http://www.youtube.com/user/MarkRosengarten#p/c/65159266CFC74682/3/XLWP03pwTYY http://www.youtube.com/user/MarkRosengarten#p/c/65159266CFC74682/3/XLWP03pwTYY

27. Practice Problem & Homework How many Joules are absorbed by 30.0g of water when its temperature is raised from 20 deg C to 40 deg C? massHeat (q) ΔT = 40 – 20 = 20 deg C

28. 28 Section 17.2 Measuring and Expressing Energy Changes OBJECTIVES: –Describe how calorimeters are used to measure heat flow. –Construct thermo-chemical equations. –Solve for enthalpy changes in chemical reactions by using heats of reaction.

29. 29 Heat and its Measurement Remember –When 2 objects of different temperatures come in contact with each other heat flows from the hotter object to the cooler one until both have reached the same temperature Calorimetry –The measurement of the amount of heat released or absorbed during a chemical reaction is called calorimetry The device used to measure the heat absorbed or released is called a calorimeter

30. 30 Calorimeter A reaction is carried out in a reaction chamber surrounded by a known mass of water Heat released by an exothermic reaction enters the water and raises the temperature Heat absorbed by an endothermic reaction is taken from the water and lowers the temperature

31. 31 Section 17.3 – Heat in Changes of State Objective: –Classify the heat of reaction change that occurs when a substance melts, freezes, boils, or condenses –Solve for the enthalpy change that occurs when a substance melts, freezes, boils, or condenses

32. 32 Points to Remember Heat is thermal energy Every piece of matter consists of very small particles that are in continuous motion When heat enters a substance it can increase the Kinetic Energy (K.E.) and make the particles move faster. –The temp of a substance is actually a measure of the average K.E. of the moving particles –An increase in temp means an increase in K.E. has occurred –A decrease in temp means a decrease in K.E. has occurred

33. 33 What does Heat in Changes of State mean? In this section we will be looking at calculations that help us determine the amount of energy needed to change a substance from one state (or phase) to another. –For example: how much energy does it take to change ice to water? –The energy we are referring to is energy in the form of heat. –So… Heat in Changes of State means Energy involved in Changing the state/phase of a substance

34. 34 Heat = q We just learned to use the formula for calculating heat: q = mCΔT This was the heat required to change the temperature of 1 gram of a substance by 1 o C Now we will look at two more formulas for calculating q, but there are some important differences you must remember…

35. 35 Important Differences in Heat Equations When using q = mCΔT, we are looking for the heat required to: –Change Temperature –With NO phase change When using any other formula for q, we are looking for heat required to: –Change phase –With NO temperature change

36. 36 Your Reference Tables

37. 37 Heat of Fusion Fusion is another name for melting Our experiences in life tell us that adding heat to something will cause it to melt. In simple terms, Heat of Fusion is the heat required to melt a substance Let’s take a closer look at what happens when we add heat to a solid substance…

38. 38 When Heating a Solid This is the Heat of Fusion 1. Heat is stored within the molecules Heat causes potential energy increase P.E.  NO Temp Δ 2. Molecules reach their limit for storing energy Added heat causes kinetic energy increase K.E.  Temp  3. Substance Reaches Temp. equal to its Melting Pt Substance will continue to absorb heat and raise its temp. until it reaches its melting point K.E.  Temp  4. Substance exists as both solid & liquid while melting Once melting temp. is reached, temp no longer rises Additional heat increases Potential energy and is used to overcomes forces holding molecules together and causes a phase change P.E.  NO K.E. Δ NO Temp Δ

39. 39 When Heating a Solid 4.Substance exists as both solid & liquid while melting –Once melting temp. is reached, temp no longer rises –Additional heat increases Potential Energy, and that additional potential energy is used to overcomes forces holding molecules together and cause a phase change. This is the Heat of Fusion When we calculate Heat of Fusion we are finding how much heat (energy) is required to melt a solid once it has reached its melting temperature.

40. 40 Heat of Fusion Heat of Fusion (H f ) –The heat (energy) absorbed by one gram of a substance in melting from a solid to a liquid –The heat of fusion of a substance is a constant For water H f = 334 J/g (see reference table B) –To calculate the amount of heat required to melt a substance at its melting point use the formula: q = mass x H f (no temperature change) Reference Table T Heat of Fusion 1:35min) http://www.youtube.com/user/MarkRosengarten#p/c/65159266CFC74682/4/jaaGqui9NVY http://www.youtube.com/user/MarkRosengarten#p/c/65159266CFC74682/4/jaaGqui9NVY

41. 41 Endothermic vs. Exothermic Video Discovery Channel: Phase Changes and the Endothermic or Exothermic Process http://player.discoveryeducation.com/index.cfm?guidAssetId=50E50883-AB32-4BF2-A7C2- 689F439573C9&blnFromSearch=1&productcode=US (2:52 min) http://player.discoveryeducation.com/index.cfm?guidAssetId=50E50883-AB32-4BF2-A7C2- 689F439573C9&blnFromSearch=1&productcode=US http://mutuslab.cs.uwindsor.ca/schurko/animations/waterphases/status_water.htm (animation video)http://mutuslab.cs.uwindsor.ca/schurko/animations/waterphases/status_water.htm http://www.rnetserv.net/trumb/concepts2.htm (good animation video)http://www.rnetserv.net/trumb/concepts2.htm

42. 42 Heat of Vaporization When liquids absorb heat at their boiling points they become vapors Heat of Vaporization (H v ) –Heat (energy) absorbed when one gram of liquid vaporizes to a gas –The heat of vaporization of a substance is a constant For water H v = 2,260 J/g (see reference Table B) –To calculate the amount of heat required to vaporize a substance at its boiling point use the formula: q = mass x H v (no temperature change) Reference table T Let’s take a closer look at what happens when you heat a liquid…

43. 43 When Heating a Liquid This is the Heat of Vaporization 1. Heat is stored within the molecules heat causes potential energy increase P.E.  NO Temp Δ 2. Molecules reach their limit for storing energy Added heat causes kinetic energy increase K.E.  Temp  3. Substance Reaches Temp. equal to its Boiling Pt Substance will continue to absorb heat and raise its temp. until it reaches its boiling point K.E.  Temp  4. Substance exists as both liquid & gas while vaporizing Once boiling temp. is reached, temp no longer rises Additional heat increases Potential energy and is used to overcomes forces holding molecules together and cause a phase change P.E.  NO K.E. Δ NO Temp Δ

44. 44 When Heating a Liquid 4.Substance exists as both liquid & gas while vaporizing –Once boiling temp. is reached, temp no longer rises –Additional heat increases Potential Energy, and that additional potential energy is used to overcomes forces holding molecules together and causes a phase change. This is the Heat of Vaporization When we calculate Heat of Vaporization we are finding how much heat (energy) is required to change a liquid to a gas once it has reached its boiling temperature.

45. 45 Think About It… Water’s heat of vaporization is 2260J/g (that’s big!). Explain in terms of energy why steam burns can be so dangerous. –If water must take in 2260 J/g when it is vaporized, it must release 2260 J/g when it condenses. H 2 0 (l)  H 2 0 (g) H v = 2260 J/g –If your skin is the recipient of that heat transfer – you get burned! http://player.discoveryeducation.com/index.cfm?guidAssetId=50E50883-AB32-4BF2-A7C2- 689F439573C9&blnFromSearch=1&productcode=US Kinetic and Potential Energy in Phase Changes (7:30 min to 8:00 min only)http://player.discoveryeducation.com/index.cfm?guidAssetId=50E50883-AB32-4BF2-A7C2- 689F439573C9&blnFromSearch=1&productcode=US

46. 46 Practice Problem At a pressure of 101.3 kilopascals and a temperature of 373 K, heat is removed from a sample of water vapor, causing the sample to change from the gaseous phase to the liquid phase. This phase change is represented by the equation below. H 2 O (g) → H 2 O (l) + heat Determine the total amount of heat released by 5.00 grams of water vapor during this phase change. [1]

47. 47 Heating Curves A heating curve illustrates the changes of state as a solid is heated. –Uses sloped lines to show an increase in temperature. –Uses plateaus to indicate a change of state. Discovery Channel Phase Changes and Temperature-Time Graphs: http://player.discoveryeducation.com/index.cfm?guidAssetId=50E50883-AB32-4BF2-A7C2- 689F439573C9&blnFromSearch=1&productcode=US (first 5:00 min only) http://player.discoveryeducation.com/index.cfm?guidAssetId=50E50883-AB32-4BF2-A7C2- 689F439573C9&blnFromSearch=1&productcode=US

48. 48 Water and Ice Ic e Water and Steam Steam -20 0 20 40 60 80 100 120 0 40120 220780800 Heating Curve for Water Heat of Fusion Temperature in Celsius Energy Added (Joules) or Time (min) Heat is added to 0 o C ice causing a phase change Chart 1

49. 49 Water and Ice Ic e Water and Steam Steam -20 0 20 40 60 80 100 120 0 40120 220780800 Heating Curve for Water Heat of Vaporization Heat is added to 100 o C water causing phase change to steam Temperature in Celsius Energy Added (Joules) or Time (min) Chart 2

50. 50 Water and Ice Ice Water and Steam Steam -20 0 20 40 60 80 100 120 0 40120 220780800 Heating Curve for Water Both Water & Steam exist at 100 o C q=mH v Temperature in Celsius Energy Added (Joules) or Time (mins) Both Ice & Water exist at 0 o C q= mH f Water (Temp  ) q=mCΔT Ice (Temp  ) Steam (Temp  ) Chart 3

51. 51 Water and Ice Ic e Water and Steam Steam -20 0 20 40 60 80 100 120 0 40120 220780800 Heating Curve for Water Temperature in Celsius Energy Added (Joules) or Time (min) Potential energy increasing, kinetic energy remaining the same http://player.discoveryeducation.com/index.cfm?guidAssetId=50E50883-AB32-4BF2-A7C2- 689F439573C9&blnFromSearch=1&productcode=UShttp://player.discoveryeducation.com/index.cfm?guidAssetId=50E50883-AB32-4BF2-A7C2- 689F439573C9&blnFromSearch=1&productcode=US Kinetic and Potential Energy in Phase Changes (1 st 4:45 min only) Chart 4 – Note: In the Notes – this slide & the next slide go under Chart 4

52. 52 Water and Ice Ic e Water and Steam Steam -20 0 20 40 60 80 100 120 0 40120 220780800 Heating Curve for Water Temperature in Celsius Energy Added (Joules) or Time (min) Heating Curve (3:20 min) http://www.youtube.com/user/MarkRosengarten#p/c/65159266CFC74682/4/jaaGqui9NVY http://www.youtube.com/user/MarkRosengarten#p/c/65159266CFC74682/4/jaaGqui9NVY Potential energy remaining the same, kinetic energy increasing Chart 4

53. 53 Cooling Curve for Water Describes the change in temperature and the amount of heat during the cooling process for water The slope of the curve is decreasing when heat is removed from the material –Mirror image of heating curve Discovery Channel Phase Changes and Temperature-Time Graphs: http://player.discoveryeducation.com/index.cfm?guidAssetId=50E50883-AB32-4BF2-A7C2- 689F439573C9&blnFromSearch=1&productcode=US (after 9:00 min mark only) http://player.discoveryeducation.com/index.cfm?guidAssetId=50E50883-AB32-4BF2-A7C2- 689F439573C9&blnFromSearch=1&productcode=US –

54. 54 Cooling Curve

55. 55 Which is Which? Endothermic Exothermic Cooling Curve Heating Curve http://player.discoveryeducation.com/index.cfm?guidAssetId=50E50883-AB32-4BF2-A7C2- 689F439573C9&blnFromSearch=1&productcode=UShttp://player.discoveryeducation.com/index.cfm?guidAssetId=50E50883-AB32-4BF2-A7C2- 689F439573C9&blnFromSearch=1&productcode=US Kinetic and Potential Energy in Phase Changes (5:20 min to 7:30 min only)

56. 56

57. 57 Following Examples are not in Class Notes Homework: –Page 510 #9-11 –Page 510 Writing Activity

58. 58 Practice Problem –A 2,000g mass of water in a calorimeter has its temperature raised 3.0 o C while an exothermic reaction is taking place. How much heat is transferred to the water by the heat of reaction?

59. 59 Practice Problem –A drinking glass and a bathtub are both filled with water at room temperature (20 o C). The glass contains 250g of water, and the bathtub contains 400,000g of water. Raising the temperature of the water in both containers requires the addition of heat. Which would require more heat, raising the temperature of the water in the drinking glass to 100 o C, or raising the temperature of the water in the bathtub by 1 o C?

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61. 61

62. 62 The following examples are not in the notes

63. 63 Practice Problem A reaction chamber inside a calorimeter contains 150g of water at 19 deg C. A reaction is permitted to take place in the chamber. After the reaction, the temp of the water is 29 deg. C. How many calories were released by the reaction?

64. 64 Do you get it? (Not in Notes) Come up with your own endothermic or exothermic objects in the world My example: I sit on a cold metal park bench. I release heat to the bench. The bench absorbs heat. I am the exothermic system, releasing heat to my environment

65. 65