Chapter: Heat and States

Transcription

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2 Table of Contents Chapter: Heat and States of Matter Section 1: Temperature and Thermal Energy Section 2: States of Matter Section 3: Transferring Thermal Energy Section 4: Using Thermal Energy

3 1 Temperature and Thermal Energy Kinetic Theory of Matter The motion of the particles in matter is described by kinetic theory of matter. Matter is composed of particles that are atoms, molecules, or ions that always are in random motion.

4 1 Temperature and Thermal Energy Temperature The temperature of a substance is a measure of the average kinetic energy of its particles. The SI unit for temperature is the Kelvin (K).

5 1 Temperature and Thermal Energy Temperature Commonly used temperature scales are the Celsius scale and the Fahrenheit scale.

6 1 Temperature and Thermal Energy Thermal Energy The sum of the kinetic and potential energies of all the particles in an object is the thermal energy of the object. The increase in an object s speed doesn t affect the random motion of its particles, so it doesn t affect its thermal energy.

7 1 Heat Temperature and Thermal Energy Heat is thermal energy that flows from something at a higher temperature to something at a lower temperature. Heat is a form of energy, so it is measured in joules.

8 1 Temperature and Thermal Energy Specific Heat The amount of thermal energy needed to raise the temperature of 1 kg of some material by 1 C is called the specific heat of the material. Specific heat is measured in joules per kilogram per degree Celsius.

9 1 Temperature and Thermal Energy Changes in Thermal Energy

10 1 Temperature and Thermal Energy Measuring Specific Heat The specific heat of a material can be measured using a device called a calorimeter. In a calorimeter, a heated sample transfers thermal energy to a known mass of water.

11 1 Temperature and Thermal Energy Measuring Specific Heat The thermal energy released by the sample is equal to the thermal energy absorbed by the water.

12 1 Question 1 Section Check How is temperature related to kinetic energy?

13 1 Answer Section Check Temperature is a measure of the average kinetic energy of the particles in an object or material. As the temperature increases, the average speed of the particles increases.

14 1 Question 2 Section Check How does thermal energy differ from kinetic energy? Answer Thermal energy is the sum of the kinetic and potential energy of all the particles in an object.

15 1 Question 3 Section Check The amount of heat that is needed to raise the temperature of 1 kg of a material by 1º C is called the of the material. A. density C. mass C. specific heat D. thermal energy

16 1 Answer Section Check The answer is C. Specific heat is measured in joules/kilogram C.

17 2 The particles of a solid are packed closely together and are constantly vibrating in place. States of Matter Four States of Matter Solid State The attractions between particles are strong and solids have a fixed volume and shape.

18 2 Liquid State States of Matter The attractive forces are strong enough to cause particles to cling together. Liquids have a definite volume, but not a definite shape.

19 2 Gas State States of Matter In a gas the forces between particles are so weak that the particles no longer cling together. Gases do not have a definite shape or volume.

20 2 Plasma State States of Matter The most common state of matter in the universe is the plasma state. Plasma is matter consisting of positively and negatively charged particles and does not have a definite shape or volume.

21 2 States of Matter Changing States Melting The temperature at which a solid begins to melt is its melting point. The amount of energy required to change 1 kg of a substance from a solid to a liquid at its melting point is known as the heat of fusion.

22 2 Freezing States of Matter The heat of fusion is also the energy released when a liquid freezes. The attractive forces are strong enough that the particles form an ordered arrangement.

23 2 Vaporization States of Matter Vaporization occurs as liquid changes into a gas. Vaporization that occurs at the surface of a liquid is called evaporation. Evaporation causes the temperature of the liquid to decrease.

24 2 Boiling States of Matter The boiling point of a liquid is the temperature at which the pressure of the vapor in the liquid is equal to the external pressure acting on its surface. The heat of vaporization is the amount of energy required for 1 kg of the liquid at its boiling point to become a gas.

25 2 Condensation States of Matter The heat of vaporization is also the amount of energy released during condensation. This graph shows the temperature change of water as thermal energy is added.

26 2 Condensation States of Matter The average kinetic energy of the water molecules doesn t change. The temperature remains constant during melting.

27 2 Condensation States of Matter After the liquid water has changed completely into a gas, the temperature of the gas increases as energy is added.

28 2 States of Matter Thermal Expansion The Thermal Expansion of Matter The increased separation between the particles results in the expansion of the object and the size of the object increases. When a material cools, the particles in the material move more slowly and become closer together.

29 2 States of Matter Thermal Expansion of Liquids The forces between the particles in liquids are weaker than the forces between the particles in a solid. The same temperature increase usually causes liquids to expand much more than solids.

30 2 States of Matter Thermal Expansion of Gases In a gas, the forces between particles are much weaker than they are in liquids. Gases expand even more than liquids for the same increase in temperature.

31 2 Question 1 Section Check is a state of matter consisting of positively and negatively charged particles that exists where the temperature is extremely high. A. Gas B. Liquid C. Plasma D. Solid

32 2 Answer Section Check The answer is C. Plasma is found in the Sun, stars, lightning bolts and neon lights.

33 2 Question 2 Section Check Most materials have a specific type of geometric arrangement. A. gaseous B. inert C. liquid D. solid

34 2 Answer Section Check The answer is D. The particles in most solids align themselves in ordered geometric patterns.

35 2 Question 3 Section Check The amount of energy required to change 1 kg of a substance from a solid to a liquid at its melting point is known as the. A. heat of energy B. heat of fusion C. heat of melting D. heat of vaporization

36 2 Answer Section Check The correct answer is B. Heat of fusion causes an ice cube to become liquid water.

37 3 Transferring Thermal Energy Ways to Transfer Thermal Energy Conduction This transfer of thermal energy between colliding particles is conduction. Kinetic energy is transferred when these faster-moving atoms collide with slowermoving particles.

38 3 Transferring Thermal Energy Thermal Conductors The rate at which thermal energy is transferred depends on the material. A material in which thermal energy is transferred easily is called a thermal conductor. Gases are poorer thermal conductors than solids or liquids.

39 3 Transferring Thermal Energy Convection Convection is the transfer of thermal energy in a fluid by the movement of fluid from place to place. A fluid expands as its temperature increases. The density of the fluid therefore decreases.

40 3 Transferring Thermal Energy Convection The warmer water is less dense and is forced upward by the sinking cooler water. The warm water transfers thermal energy to the cooler water around it.

41 3 Transferring Thermal Energy Convection When the warm water cools, it becomes denser than the surrounding water and sinks. The rising and sinking water forms a convection current.

42 3 Transferring Thermal Energy Radiation Radiation is the transfer of energy by electromagnetic waves. Radiation can pass through solids, liquids, and gases, but the transfer of energy by radiation is most important in gases.

43 3 Transferring Thermal Energy Radiation When radiation strikes a material, some energy is absorbed, some is reflected, and some may be transmitted through the material.

44 3 Transferring Thermal Energy Thermal Insulators A material in which thermal energy moves slowly is a thermal insulator. Materials that are good conductors of thermal energy, such as metals are poor thermal insulator.

45 3 Question 1 Section Check Describe the difference between conduction and convection.

46 3 Answer Section Check Conduction transfers thermal energy without transferring matter. In convection, the more energetic particles move from one place to another. Convection currents result when heated fluid rises and cooler fluid sinks.

47 3 Question 2 Section Check is the transfer of energy by electromagnetic waves. Answer The transfer of energy by electromagnetic waves is radiation. Radiation is how Earth gets heat from the Sun.

48 3 Question 3 Section Check Which of the following is the least effective insulator? A. air B. fiberglass C. metal D. wood

49 3 Answer Section Check The answer is C. Metals are good conductors of heat. And heat flows more rapidly in them.

50 4 Using Thermal Energy How is thermal energy used? Heating Systems Forced-Air Systems Fuel is burned in a furnace and heats a volume of air. A fan blows the heated air through a series of large pipes called ducts. The ducts lead to openings called vents in each room.

51 4 Using Thermal Energy Radiator Systems A radiator is a closed metal container that contains hot water or steam. The thermal energy contained in the hot water or steam is transferred to the air surrounding the radiator by conduction.

52 4 Using Thermal Energy Electric Heating Systems In an electric heating system, electrically heated coils placed in floors and in walls heat the surrounding air by conduction and convection.

53 4 Using Thermal Energy Thermodynamics Heating and Work Increase Thermal Energy A system is anything you can draw a boundary around. The energy transferred to a system is the amount of energy flowing into the system across the boundary. The work done on a system is the work done by something outside the system s boundary.

54 4 Using Thermal Energy The First Law of Thermodynamics According to the first law of thermodynamics, the increase in thermal energy of a system equals the work done on the system plus the thermal energy transferred to the system. The increase in energy of a system equals the energy added to the system.

55 4 Using Thermal Energy Closed and Open Systems A system is an open system if thermal energy flows across the boundary or if work is done across the boundary. If no thermal energy flows across the boundary and no outside work is done, the system is a closed system.

56 4 Using Thermal Energy The Second Law of Thermodynamics The second law of thermodynamics states it is impossible for thermal energy to flow from a cool object to a warmer object unless work is done.

57 4 Using Thermal Energy Converting Thermal Energy to Work No device or process can convert thermal energy completely into work.

58 4 Heat Engines Using Thermal Energy A device that converts thermal energy into work is called a heat engine. When thermal energy is converted into work, some thermal energy always is transferred to the surroundings.

59 4 Using Thermal Energy Internal Combustion Engines The heat engine in a car is an internal combustion engine. Each cylinder contains a piston that moves up and down. Each up or down movement of the piston is called a stroke.

60 4 Using Thermal Energy Internal Combustion Engines

61 4 Using Thermal Energy Moving Thermal Energy Liquid coolant is pumped through an expansion valve and changes into a gas. The cold gas is pumped through pipes inside the refrigerator. The coolant absorbs thermal energy and the inside of the refrigerator cools.

62 4 Entropy Using Thermal Energy According to the laws of thermodynamics, work can be converted completely into thermal energy, but thermal energy cannot be converted completely into work. Entropy is a measure of how spread out, or dispersed, energy is. Entropy increases when energy becomes more spread out and less concentrated.

63 4 Using Thermal Energy Entropy Always Increases According to the entropy principle, all events that occur cause the entropy of the universe to increase. The energy that becomes spread out is no longer useable.

64 4 Question 1 Section Check The study of the relationship among thermal energy, heat and work is. A. electrical engineering B. graphical analysis C. specific heat D. thermodynamics

65 4 Answer Section Check The answer is D, thermodynamics.

66 4 Question 2 Section Check According to, the increase in thermal energy of a system equals the work done on the system plus the heat transferred to the system. A. Newton s First Law B. Newton s Second Law C. the first law of thermodynamics D. the second law of thermodynamics

67 4 Answer Section Check The answer is C. Doing work on a system is a way of adding energy to a system.

68 4 Question 3 Section Check How does a refrigerator work? Answer The refrigerator coolant absorbs thermal energy from inside the refrigerator and releases it into the surrounding air.

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70 End of Chapter Summary File