Hewitt/Lyons/Suchocki/Yeh Conceptual Integrated Science

1. Hewitt/Lyons/Suchocki/YehConceptual Integrated Science Chapter 6 HEAT

2. This lecture will help you understand: • The Kinetic Theory of Matter • Temperature • Absolute Zero • What Is Heat? • Quantity of Heat • The Laws of Thermodynamics • Entropy • Specific Heat Capacity • Thermal Expansion • Expansion of Water • Heat Transfer: Conduction • Heat Transfer: Convection • Heat Transfer: Radiation • Emission of Radiant Energy • Absorption of Radiant Energy

3. The Kinetic Theory of Matter Kinetic Theory of Matter: Matter is made up of tiny particles (atoms or molecules) that are always in motion. Thermal Energy: The total energy (kinetic and potential) of the submicroscopic particles that make up a substance.

4. Temperature Temperature is defined as the measure of hotness or coldness of an object (degrees Celsius, or degrees Fahrenheit, or kelvins). is related to the average translational kinetic energy per molecule in a substance.

5. Temperature Thermometer is an instrument that measures temperature by comparing the expansion and contraction of a liquid as it gains or loses thermal energy. Infrared thermometer measures temperature by the radiation a substance emits.

6. Temperature Temperature has no upper limit. Temperature of a substance is registered on a liquid-base thermometer when the substance has reached thermal equilibrium with the thermometer.

7. Temperature Three different temperature scales differ in zero point and divisions: • Celsius scale freezing point of water: 0C boiling point of water: 100C division: 100 degree units

8. Temperature • Fahrenheit scale freezing point of water: 32 F boiling point of water: 212 F division: 180 degree units • Kelvin scale (used in scientific research) freezing point of water: 273 K boiling point of water: 373 K division: same-size increments as Celsius scale

9. Temperature CHECK YOUR NEIGHBOR There is twice as much molecular kinetic energy in 2 liters of boiling water as in 1 liter of boiling water. Which will be the same for both? A. Temperature. • Thermal energy. • Both of the above. • None of the above.

10. Temperature CHECK YOUR ANSWER There is twice as much molecular kinetic energy in 2 liters of boiling water as in 1 liter of boiling water. Which will be the same for both? A. Temperature. • Thermal energy. • Both of the above. • None of the above. Explanation: Average kinetic energy of molecules is the same, which means temperature is the same for both.

11. Absolute Zero Absolute zero or zero K is the lowest limit of temperature at –273C where molecules have lost all available kinetic energy. A substance cannot get any colder.

12. What Is Heat? Heat is defined as a flow of thermal energy due to a temperature difference. The direction of heat flow is from a higher-temperature substance to a lower-temperature substance.

13. What Is Heat? CHECK YOUR NEIGHBOR If a red hot thumbtack is immersed in warm water, the direction of heat flow will be from the A. warm water to the red hot thumbtack. • red hot thumbtack to the warm water. • no heat flow. • not enough information.

14. What Is Heat? CHECK YOUR ANSWER If a red hot thumbtack is immersed in warm water, the direction of heat flow will be from the A. warm water to the red hot thumbtack. • red hot thumbtack to the warm water. • no heat flow. • not enough information.

15. Quantity of Heat Heat is measured in units of energy—joules or calories. calorie is defined as the amount of heat needed to raise the temperature of 1 gram of water by 1 Celsius degree. 4.18 joules = 1 calorie so 4.18 joules of heat will change that temperature of 1 gram of water by 1 Celsius degree.

16. Quantity of Heat Energy rating of food and fuel is measured by energy released when they are metabolized. Kilocalorie: Heat unit for labeling food One kilocalorie or Calorie (with a capital C) is the heat needed to change the temperature of 1 kilogram of water by 1 degree Celsius.

17. Quantity of Heat CHECK YOUR NEIGHBOR The same quantity of heat is added to different amounts of water in two equal-size containers. The temperature of the smaller amount of water A. decreases more. • increases more. • does not change. • not enough information.

18. Quantity of Heat CHECK YOUR ANSWER The same quantity of heat is added to different amounts of water in two equal-size containers. The temperature of the smaller amount of water A. decreases more. • increases more. • does not change. • not enough information.

19. Quantity of Heat CHECK YOUR NEIGHBOR You heat a half-cup of tea and its temperature rises by 4C. How much will the temperature rise if you add the same amount of heat to a full cup of tea? A. 0C. • 2C. • 4C. • 8C.

20. Quantity of Heat CHECK YOUR ANSWER You heat a half-cup of tea and its temperature rises by 4C. How much will the temperature rise if you add the same amount of heat to a full cup of tea? A. 0C. • 2C. • 4C. • 8C.

21. The Laws of Thermodynamics First Law of Thermodynamics: Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred. When thermal energy transfers as heat, it does so without net loss or gain.

22. The Laws of Thermodynamics Second Law of Thermodynamics: Heat never spontaneously flows from a lower-temperature substance to a higher-temperature substance. Heat can be made to flow the opposite way only when work is done on the system or by adding energy from another source.

23. The Laws of Thermodynamics Third Law of Thermodynamics: No system can reach absolute zero.

24. The Laws of Thermodynamics CHECK YOUR NEIGHBOR When work is done on a system, compressing air in a tire pump, for example, the temperature of the system A. increases. • decreases. • remains unchanged. • is no longer evident.

25. The Laws of Thermodynamics CHECK YOUR ANSWER When work is done on a system, compressing air in a tire pump, for example, the temperature of the system A. increases. • decreases. • remains unchanged. • is no longer evident. Explanation: In accord with the first law of thermodynamics, work input increases the energy of the system.

26. Entropy Entropy is a measure of the disorder of a system. Whenever energy freely transforms from one form to another, the direction of transformation is toward a state of greater disorder and, therefore, toward one of greater entropy. The greater the disorder the higher the entropy.

27. Entropy Second law of thermodynamics — restatement: Natural systems tend to disperse from concentrated and organized-energy states toward diffuse and disorganized states. Energy tends to degrade and disperse with time. The total amount of entropy in any system tends to increase with time.

28. Entropy CHECK YOUR NEIGHBOR Your room gets messier each week. In this case, the entropy of your room is A. increasing. • decreasing. • hanging steady. • nonexistent.

29. Entropy CHECK YOUR ANSWER Your room gets messier each week. In this case, the entropy of your room is A. increasing. • decreasing. • hanging steady. • nonexistent. Comment: If your room became more organized each week, then entropy would decrease in proportion to the effort expended.

30. Specific Heat Capacity Specific heat capacity is defined as the quantity of heat required to change the temperature of 1 unit mass of a substance by 1 degree Celsius. • thermal inertia that indicates the resistance of a substance to a change in temperature. • sometimes called specific heat.

31. Specific Heat CHECK YOUR NEIGHBOR Which has the higher specific heat, water or land? A. Water. • Land. • Both of the above are the same. • None of the above.

32. Specific Heat CHECK YOUR ANSWER Which has the higher specific heat, water or land? A. Water. • Land. • Both of the above are the same. • None of the above. Explanation: A substance with small temperature changes for large heat changes has a high specific heat capacity. Water takes much longer to heat up in the sunshine than does land. This difference is a major influence on climate.

33. Thermal Expansion Thermal Expansion When the temperature of a substance is increased, its particles jiggle faster and move farther apart. All forms of matter generally expand when heated and contract when cooled.

34. Thermal Expansion CHECK YOUR NEIGHBOR When stringing telephone lines between poles in the summer, it is advisable to allow the lines to A. sag. • be taut. • be close to the ground. • allow ample space for birds.

35. Thermal Expansion CHECK YOUR ANSWER When stringing telephone lines between poles in the summer, it is advisable to allow the lines to A. sag. • be taut. • be close to the ground. • allow ample space for birds. Explanation: Telephone lines are longer in a warmer summer and shorter in a cold winter. Hence, they sag more on hot summer days than in winter. If the lines are not strung with enough sag in summer, they might contract too much and snap during the winter—especially when carrying ice.

36. Expansion of Water Expansion of Water When water becomes ice, it expands. Ice has open-structured crystals resulting from strong bonds at certain angles that increase its volume. This make ice less dense than water.

37. Expansion of Water Water between 0C and 4C does not expand with temperature. As the temperature of 0 water rises, it contracts until it reaches 4C. Thereafter, it expands. Water is at its smallest volume and greatest density at 4C. When 0C water freezes to become ice, however, it has its largest volume and lowest density.

38. Expansion of Water Volume changes for a 1-gram sample of water.

39. Expansion of Water CHECK YOUR NEIGHBOR When a sample of 0C water is heated, it first A. expands. • contracts. • remains unchanged. • not enough information.

40. Expansion of Water CHECK YOUR ANSWER When a sample of 0C water is heated, it first A. expands. • contracts. • remains unchanged. • not enough information. Explanation: Water continues to contract until it reaches a temperature of 4C. With further increase in temperature beyond 4C, water then expands.

41. Expansion of Water CHECK YOUR NEIGHBOR When a sample of 4C water is cooled, it A. expands. • contracts. • remains unchanged. • not enough information.

42. Expansion of Water CHECK YOUR ANSWER When a sample of 4C water is cooled, it A. expands. • contracts. • remains unchanged. • not enough information. Explanation: Parts of the water will crystallize and occupy more space.

43. Heat Transfer Processes of thermal energy transfer: • conduction • convection • radiation

44. Heat Transfer: Conduction Conduction occurs predominately in solids where the molecules remain in relatively restricted locations.

45. Heat Transfer: Conduction Example: When one end of a solid is placed near a heat source, electrons and adjacent molecules gain kinetic energy and start to move faster and farther. They collide with neighboring molecules and transfer some of their kinetic energy to them. These molecules then interact with other neighboring molecules, and thermal energy is gradually transferred along the solid.

46. Heat Transfer: Conduction Good conductors: • composed of atoms with “loose” outer electrons • known as poor insulators • examples—all metals to varying degrees Poor conductors: • delay the transfer of heat • known as good insulators • examples—wood, wool, straw, paper, cork, Styrofoam, liquid, gases, air, or materials with trapped air

47. Heat Transfer: Conduction No insulator can totally prevent heat from getting through it. An insulator reduces the rate at which heat penetrates.

48. Heat Transfer: Conduction CHECK YOUR NEIGHBOR If you hold one end of a metal bar against a piece of ice, the end in your hand will soon become cold. Does cold flow from the ice to your hand? A. Yes. • In some cases, yes. • No. • In some cases, no.

49. Heat Transfer: Conduction CHECK YOUR ANSWER If you hold one end of a metal bar against a piece of ice, the end in your hand will soon become cold. Does cold flow from the ice to your hand? A. Yes. • In some cases, yes. • No. • In some cases, no. Explanation: Cold does not flow from the ice to your hand. Heat flows from your hand to the ice. The metal is cold to your touch, because you are transferring heat to the metal.

50. Heat Transfer: Convection Convection: • occurs in liquids and gases • involves the movement of warmer gases or liquids to cooler surroundings Two characteristics of convection: • the ability of flow—carrying thermal energy with the fluid • the ability of warm fluid to rise in cooler surroundings