Temperature Energy and Heat

Transcription

1 CHAPTER 3 Temperature Energy and Heat 3.1 Temperature

2 What is temperature? Why is temperature important in chemistry? How is energy related to temperature? Temperature

3 Milk fat particles are being pushed around by water molecules At room temperature, atoms and molecules are in constant motion Brownian motion Temperature

4 Grains of sand stand still but the individual atoms are in constant, random motion. kinetic energy: the energy of motion. temperature: a measure of the average kinetic energy of atoms or molecules Temperature

5 Temperature is an average Some molecules have more kinetic energy than the average. Some molecules have less kinetic energy than the average. Temperature is the measure of the average kinetic energy of atoms or molecules, thus as ke increases so does the temperature Temperature

6 Temperature scales Temperature

7 Temperature scales Water boils Water freezes How can we go back and forth between the two scales? Temperature

8 What temperature in Celsius is the same as 100 o F? Asked: Given: Relationships: Solve: Answer: Temperature in o C 100 o F 5 TC TF TC o F is the same temperature as 37.8 o C o C Temperature

9 What is the Fahrenheit equivalent of 15 o C? Asked: Given: Relationships: Solve: Temperature in o F 15 o C T F TF 5 Tc o F 9 Answer: 15 o C is the same temperature as 59 o F Temperature

10 All thermometers are based on a physical property that changes with temperature. Thermal expansion: - Mercury thermometers - Alcohol thermometers Electrical sensors: - Thermistor - Thermocouple Temperature

11 All thermometers are based on a physical property that changes with temperature. Thermal expansion: - Mercury thermometers - Alcohol thermometers Electrical sensors: - Thermistor - Thermocouple The temperature probe in the Lab-Master uses a thermistor Temperature

12 kinetic energy: the energy of motion. temperature: a measure of the average kinetic energy of atoms or molecules. heat: thermal energy, the total energy in random molecular motion, energy resulting from temperature Temperature

13 Temperature While temperature is related to thermal energy, there is no absolute correlation between the amount of thermal energy (heat) of an object and its temperature. Temperature measures the concentration of thermal energy in an object in much the same way that density measures the concentration of matter in an object. As a result, a large object will have a much lower temperature than a small object with the same amount of thermal energy. Different materials respond to changes in thermal energy with more or less dramatic changes in temperature. The temperature of a material is a measure of the average kinetic energy of the molecules that make up that material. Absolute zero is defined as the temperature at which the molecules have zero kinetic energy, which is why it is impossible for anything to be colder Temperature

14 Heat Heat is a measure of how much thermal energy is transmitted from one body to another. We cannot say a body has a certain amount of heat any more than we can say a body has a certain amount of work. While both work and heat can be measured in terms of joules, they are not measures of energy but rather of energy transfer. A hot water bottle has a certain amount of thermal energy; when you cuddle up with a hot water bottle, it transmits a certain amount of heat to your body Temperature

15 Absolute zero At absolute zero the kinetic energy is essentially zero. 3 different scales Temperature

16 Unit conversion T Kelvin T Celsius Temperature

17 Unit conversion Convert 27 o C into kelvins. Asked: Given: Temperature in kelvin 27 o C Relationships: T Kelvin T Celsius 273 Solve: TK K Answer: 300 K is the same temperature as 27 o C Temperature

18 Molecules are in constant, random motion. This affects temperature. Three temperature scales: T Fahrenheit 9 T 5 Celsius 32 T Celsius 5 9 T Fahrenheit 32 T Kelvin T Celsius Temperature

19 CHAPTER 3 Temperature Energy and Heat 3.2 Heat and Thermal Energy Temperature

20 We know now that heat is not the same thing as temperature. Measured in o F, o C, K Measured in? Temperature

21 Heat can be measured in joules (J). The joule is the fundamental SI unit of energy and heat Temperature

22 Heat can be measured in calories. It takes 1 calorie to raise 1 g of water by 1 o C. 1 Calorie = 1 kilocalorie = 1,000 calories Temperature

23 Heat can be measured in British thermal units (BTU) Temperature

24 joules (J) Heat can be measured in calories British thermal units (BTU) 1 calorie = joules 1 BTU = 1,055 joules Temperature

25 second law of thermodynamics: energy (heat) spontaneously flows from higher temperature to lower temperature Temperature

26 Thermal equilibrium A condition where the temperatures are the same and heat no longer flows from one material to another. Humans are most comfortable at 25*C because the rate of heat flow out of the body matches the rate at which the body generates heat. Temperatures below 25*C will feel cold because the body loses heat too quickly Temperatures above 25*C will feel hot because the body will retain heat rather than lose it Temperature

27 SURROUNDING Matter and energy flow through the system Only energy can flow through the system. Neither matter nor energy can be exchanged or flow Temperature

28 first law of thermodynamics: energy can neither be created nor destroyed Temperature

29 first law of thermodynamics: energy can neither be created nor destroyed. The energy inside an isolated system is constant. The energy lost by a system must be gained by the surroundings or another system Temperature

30 What happens when hot and cold water are not allowed to mix but are allowed to exchange energy? Does one side stay hot and one side stays cold? Temperature

31 Thermal equilibrium The system reaches thermal equilibrium at 45*C Since both sides have the same mass of water, they will reach equilibrium at the average of the two temperatures = Temperature

32 specific heat: the quantity of energy it takes per gram of a certain material to raise the temperature by one degree Celsius. Specific heat of water: J/(g oc) Specific heat of gold: J/(g oc) Temperature

33 Why do different metals have different specific heats? One reason is: Ag = g/mol Al = g/mol Temperature

34 A metal-working process needs to heat steel from room temperature (20 o C) to 2,000 o C. If the mass of steel is 100 g, how much heat is required? A table is located on page 83 that lists the specific heat of common substances Temperature

35 Temperature

36 A metal-working process needs to heat steel from room temperature (20 o C) to 2,000 o C. If the mass of steel is 100 g, how much heat is required? Asked: Given: Relationships: Solve: Answer: Quantity of heat o 100 g of steel, cp J g C temperature difference is 2,000 o C 20 o C E mc T T p 2 1 o C E 100 g J g ,060 J It takes 93,060 joules to raise the temperature of 100 g of steel to 2,000 o C, assuming no heat gets lost during the process (which is not a very good assumption!) Temperature

37 *** NOT on test.woohoo A mass of 300 grams of water at 80 o C cools down to 20 o C. Assume all the heat from the water is absorbed by 100 m 3 of air (a small room) with a mass of 100,000 g. What is the temperature change in the air? Asked: Given: Relationships: Solve: Temperature change in o C 300 g of water [c p = J/(g oc)], change of 60 o C (80 o C 20 o C), and 100,000 g of air [c p = J/(g oc)] E mc T T p 2 1 o o Energy lost by the water 300 g J g C 60 C 75,312 J Energy gained by the air energy lost by water 75,312 J Temperature change of air 75,312 J o 100,000 g J g C Answer: The air in the room gets warmer by about 0.75 o C o C Temperature

38 conduction: the flow of heat energy through the direct contact of matter Temperature

39 Would you describe the glass of the test tube as a thermal conductor or a thermal insulator? Thermal equilibrium was reached (60oC both inside and outside the test tube). Because the test tube allowed heat to flow, it is a thermal conductor Temperature

40 Would you describe the styrofoam cup of the test tube as a thermal conductor or a thermal insulator? Temperature

41 Temperature is measured in: o F, o C, kelvin Heat is measured in: joules (J), calories, British thermal units (BTU) first law of thermodynamics: energy can neither be created nor destroyed. second law of thermodynamics: energy (heat) spontaneously flows from higher temperature to lower temperature Temperature

42 Temperature CHAPTER 3 Energy and Heat 3.3 Phase Changes Temperature

43 Temperature

44 Kelvin Scale The Bose-Einstein state of matter was the only one created while your parents were alive. In 1995, two scientists, Cornell and Weiman, finally created the condensate. Physicists acknowledge they can never reach the coldest conceivable temperature, known as absolute zero and long ago calculated to be minus F. To physicists, temperature is a measure of how fast atoms are moving, a reflection of their energy and absolute zero is the point at which there is absolutely no heat energy remaining to be extracted from a substance Temperature

45 When you get to a temperature near absolute zero, something special happens. Atoms begin to clump. The whole process happens at temperatures within a few billionths of a degree, so you won't see this at home. When the temperature becomes that low, the atomic parts can't move at all. They lose almost all of their energy. Since there is no more energy to transfer (as in solids or liquids), all of the atoms have exactly the same levels, like twins. The result of this clumping is the BEC. The group of rubidium atoms sits in the same place, creating a "super atom." There are no longer thousands of separate atoms. They all take on the same qualities and, for our purposes, become one blob Temperature

46 ScienceCasts- The Coolest Spot in the Universe Temperature

47 Where do the drops of water on the cold window come from? Is this water? Temperature

48 A phase change is a physical change No chemical reaction is involved Frozen or boiled water molecules are still water molecules Melted iron is still iron. Molecules or atoms are simply rearranged! Temperature

49 Phase changes Temperature

50 Phase changes Melting point Boiling point Temperature scale Temperature

51 How can we move from solid to liquid, and from liquid to gas? Temperature

52 How can we move from solid to liquid, and from liquid to gas? By overcoming the intermolecular forces. How? Temperature

53 Heat of fusion Heat of vaporization Temperature

54 Adding more heat may not increase the temperature during melting or boiling! Temperature

55 H f (joules/gram) Heat of fusion Heat of vaporization H v (joules/gram) Add heat to go from solid to liquid, and from liquid to gas Temperature

56 H f (joules/gram) Heat of fusion Heat of vaporization H v (joules/gram) Remove heat to go from gas to liquid, and from liquid to solid Temperature

57 Heat of fusion H f (J/g) Heat of vaporization H v (J/g) Overcome intermolecular forces Overcome intermolecular forces Temperature

58 phase change: a change in the way molecules are physically arranged in space without chemically changing the molecules themselves. For example, molecules are tightly packed together in a liquid and far apart from each other in a gas. heat of vaporization, H v : the energy required to change the phase of one gram of a material from liquid to gas, or gas to liquid at constant temperature and constant pressure at the boiling point. heat of fusion, H f : the energy required to change the phase of one gram of a material from liquid to solid or solid to liquid at constant temperature and constant pressure at the melting point Temperature

59 ENERGY CAN BE RELEASED OR ABSORBED DURING PHASE CHANGES!!! Energy expended during a phase change MUST be conserved and is no longer available to change the temperature of the system!!! Temperature

60 Ice cubes with a temperature of 25 o C are used to cool off a glass of punch. Which absorbs more heat: warming up the ice or melting the ice into water? The specific heat of ice is 2.0 J/(g oc) Temperature

61 Ice cubes with a temperature of 25 o C are used to cool off a glass of punch. Which absorbs more heat: warming up the ice or melting the ice into water? The specific heat of ice is 2.0 J/(g oc). Asked: Given: Which absorbs more heat, warming ice by 25 o C or melting it? The ice starts at 25 o C. The specific heat of ice is 2.0 J/(g oc). H f (water) = 335 J Relationships: E = mc p (T 2 T 1 ) and E = m H f Temperature

62 Ice cubes with a temperature of 25 o C are used to cool off a glass of punch. Which absorbs more heat: warming up the ice or melting the ice into water? The specific heat of ice is 2.0 J/(g oc). Asked: Given: Which absorbs more heat, warming ice by 25 o C or melting it? The ice starts at 25 o C. The specific heat of ice is 2.0 J/(g oc). H f (water) = 335 J Relationships: E = mc p (T 2 T 1 ) and E = m H f Solve: First, let s calculate the energy that it takes to warm up a gram of ice from 25 o C to 0 o C o o E mcp T T g J g C 25 C 50 J So it takes 50 J to warm up 1 g of ice from 25 o C to 0 o C. The same gram of ice takes 335 J to melt into liquid water Temperature

63 Ice cubes with a temperature of 25 o C are used to cool off a glass of punch. Which absorbs more heat: warming up the ice or melting the ice into water? The specific heat of ice is 2.0 J/(g oc). Asked: Answer: Given: Which absorbs more heat, warming ice by 25 o C or melting it? Changing phase (melting) absorbs 335 J per gram of ice but The warming ice starts the ice at only 25oC. absorbs The specific 50 J/g. The heat phase of ice is change 2.0 J/(g oc). is H responsible f (water) = for 335 most J of ice s cooling effect on drinks! Relationships: E = mc p (T 2 T 1 ) and E = m H f Solve: First, let s calculate the energy that it takes to warm up a gram of ice from 25 o C to 0 o C o o E mcp T T g J g C 25 C 50 J So it takes 50 J to warm up 1 g of ice from 25 o C to 0 o C. The same gram of ice takes 335 J to melt into liquid water Temperature

64 Where did the coffee go? You left a cup of coffee in your warm room, then took off for the weekend. Did someone finish your coffee while you were away? Temperature

65 evaporation: a phase change from liquid to gas at a temperature below the boiling point Temperature

66 Is the glass sweating? Where does the water on the outside of the glass come from? Temperature

67 Heat of vaporization Water molecules in the air (gas) lose energy when in contact with the cold glass. This loss in thermal energy causes a phase change Temperature

68 Where do the drops of water on the cold window come from? Is this water? Temperature

69 condensation: a phase change from gas to liquid; a substance in its gas phase may condense at a temperature below its boiling point. latent heat: thermal energy that is absorbed or released during a phase change Temperature

70 In Denver, Colorado, water boils at 95 o C (203 o F) instead of the usual 100 o C (212 o F). Why? Temperature

71 In Denver, Colorado, water boils at 95 o C (203 o F) instead of the usual 100 o C (212 o F) Temperature

72 A phase equilibrium diagram shows the relationship between temperature and pressure and the resulting phase of matter! Phase equilibrium diagram of water Melting point Freezing point Temperature

73 Temperature

74 Sublimation is the phase change as a substance changes from a solid to a gas without passing through the intermediate state of a liquid. Deposition is the phase change as a substance changes from a gas to a solid without passing through the intermediate state of a liquid. TRIPLE POINT - The temperature and pressure at which the solid, liquid, and gas phases exist simultaneously. CRITICAL POINT The temperature above which a substance will always be a gas regardless of the pressure. NOTE: o The solid phase is more dense than the liquid phase. (EXCEPTION WATER) o The line between the solid and gas phases is the equilibrium of solid and gas phases at that specific pressure and temperature, i.e. a curve of all the deposition/sublimation points. o The line between the solid and liquid phases is the equilibrium of solid and liquid phases at that specific pressure and temperature, i.e. a curve of all the freezing/melting points. o The line between the liquid and gas phases is the equilibrium of liquid and gas phases at that specific pressure and temperature, i.e. a curve of all the vaporization/condensation points Temperature

75 TRIPLE POINT = the temperature and pressure where the solid, liquid and gas can all coexist in equilibrium WOW. Triple point Temperature