Catalyst

1. Catalyst • A sample of water loses 96 Joules of heat when it cools down from 70 °C to 45 °C. What is the mass of the water sample? The specific heat of water is 4.18 J/g/°C. • A 47 g piece of metal with an initial temperature of 90 °C is placed in a calorimeter that holds 60 g of water. The initial temperature of the water is 60 °C and the final temp of the system is 75 °C. What is the specific heat of the metal?

2. Today’s Agenda

3. Thermal Energy • Thermal energy is another word for heat. • Molecules are always moving. Thermal energy is a measure of how fast these molecules are moving. • The faster they are moving, the more temperaturean object has.

4. Heat Transfer • The Law of Conservation of Energy states energy can’t be created or destroyed. • Since energy can be transferred (but never destroyed), thermal energy (heat) can also be transferred. • Heat will travel from an area of high heatto an area of low heat (but never the other way around). • Like saying it goes from hot  cold

5. Heat Transfer • There are three types of heat transfer: conduction, convection and radiation. ConductionConvectionRadiation

6. Conduction • Imagine it is very cold outside and you walk to school. As soon as you come inside, I hand you a mug of hot chocolate. What happens to your cold hands?

7. Conduction • Conduction – Transfer of heat through matter by the direct contact of particles. • Since molecules are always moving, whenever there is direct contact between two things, the molecules from one object will collide with the molecules of the other object.

8. Conduction • The fast particles (the hot ones) will transfer some of their kinetic energy to the slow particles (the cold ones). This will make the slow particles move faster (and therefore have more heat). • This happens most often in solids, because in solids the particles are packed closely together.

9. The Process

10. The Process for Bulk Objects

11. Examples of Conduction • What are some examples of heat transfer through direct contact can you think of? • Once the class thinks of some examples, draw one of those in the box in your notes. Make sure to label the direction of heat transfer using arrows (from hot to cold).

12. Convection • Imagine you are in a pool on a hot day. You are hanging out in a group of friends. All of a sudden, the water gets warm around you. Your best friend shouts out, “Ew… Gross!” • What do you think happened? • Is this a method of heat transfer?

13. Convection • One way that liquids and gases differ from solids is that they can flow. (What does flow mean?) This makes them fluids. • Convection – heat transfer in a fluid by movement of heated particles.

14. Convection • In convection, the particles actually move from one place to another. • The moving fluid carries energy • How is this different than conduction?

15. Heating a Pot of Water • As the water at the bottom becomes hot, it is less dense and rises which takes the place of the cold water above • Once the cold water is heated, it begins to rise causing the circulation

16. Examples of Convection • What are some examples of heat transfer through fluids can you think of? • Once the class thinks of some examples, draw one of those in the box in your notes. Make sure to label the direction of heat flow (from hot to cold).

17. Radiation • Where does all of earth’s heat energy come from? • Conduction and convection require matter (solid, liquid, or gas) to transfer heat. • However, there is almost no matter (only empty space) between us and the sun. So how does the sun get heat energy to us?

18. Radiation • Radiation is the transfer of energy by electromagnetic waves. • What is interesting about radiation is that it does NOT require any matter. (It can happen in empty space!)

19. Radiation • The hotter the object, the more it radiates! • Which would radiate off more energy: a coffee mug or the sun? • Thermal radiation is a form of heat transfer because the electromagnetic radiation emitted from the source carries energy away from the source to surrounding (or distant) objects.

20. Radiation Photograph • Image was taken by a thermal imaging camera. • The camera detects the radiation emitted by objects and represents it by means of a color photograph. • The hotter colors represent areas of objects that are emitting thermal radiation at a more intense rate

21. Examples of Radiation • The best (and most common) examples of radiation are from the sun and from heat lamps. • Draw one of those in the box in your notes. Make sure to label the direction of heat transfer (from hot to cold).

22. Heat transfer • Can we have 3 methods of heat transfer at once? YES!

24. Check for Understanding • Which method of heat transfer involves movement of particles through a fluid? • Conduction • Convection • Radiation

25. Check for Understanding • Which method of heat transfer involves direct contact of particles? • Conduction • Convection • Radiation

26. Check for Understanding • Which method of heat transfer involves electromagnetic waves? • Conduction • Convection • Radiation

27. Check for Understanding • Which method of heat transfer describes how a pot of water heats up? • Conduction • Convection • Radiation

28. Check for Understanding • Which method of heat transfer occurs when you touch your cold hands to something warm? • Conduction • Convection • Radiation

29. Check for Understanding • Which method of heat transfer describes why your car heats up on a hot day? • Conduction • Convection • Radiation

30. Today’s Agenda

31. First Law of Thermodynamics • The First Law of Thermodynamics states that in a closed system, energy can neither be created nor destroyed, only transformed or transferred. There is an energy balance in the universe. • What does this sound a lot like???

32. Connection to Heat • Whenever heat is added to a system, it transforms into some other form of energy. • That form of usable energy is WORK.

33. Conservation of Energy Some visual examples of this principle

34. 1st Law Equation Q = DE – W(DE = EFinal– Einitial)

35. 1st Law Equation Q = heat added TO THE SYSTEM DE = change in internal energy (DE = EFinal– Einitial) W = Work done ON THE SYSTEM If the system does work, W is NEGATIVE Q = DE – W

36. Example A total of 135 J of work is done on a gaseous refrigerant as it undergoes compression. If the internal energy of the gas increases from 0 J to 156 J during the process, what is the total amount of energy removed from the gas by heat?

37. Example Answer • A total of 135 J of work is done on a gaseous refrigerant as it undergoes compression. If the internal energy of the gas increases from 0 J to 156 J during the process, what is the total amount of energy removed from the gas by heat? • Q = ΔE – W • Q = 156 J – 135 J • Q = 21 J

38. Guided Practice An object has an initial internal energy of 48 J. The internal energy increases to 73 J when 38 J of work is done. What is the amount of energy in the form of heat that was gained by the system during this?

39. Guided Practice Answer • An object has an initial internal energy of 48 J. The internal energy increases to 73 J when 38 J of work is done. What is the amount of energy in the form of heat that was gained by the system during this? • Q = ΔE – W • Q = (EF – EI) – W • Q = (73 J – 48 J) – 38 J • Q = -13 J

40. Step Up The internal energy of a system is initially 27 J. After 33 J of heat is added to the system, the internal energy is measured to be 86 J. How much work was done on the system?

41. Step Up Answer • The internal energy of a system is initially 27 J. After 33 J of heat is added to the system, the internal energy is measured to be 86 J. How much work was done on the system? • Q = ΔE – W • Q = (EF – EI) – W • 33 J = (86 J – 27 J) – W • 33 J = 59 J – W • W = 59 J – 33 J • W = 26 J

42. Step Further • The internal energy of a system is initially 45 J. A total of 28 J of energy is added to the system by heat while the system does -31 Jof work. What is the system’s final internal energy? • Q = ΔE – W • Q = (EF – EI) – W

43. Step Further Answer • The internal energy of a system is initially 45 J. A total of 28 J of energy is added to the system by heat while the system does -31 Jof work. What is the system’s final internal energy? • Q = ΔE – W • Q = (EF – EI) – W • 28 J = (EF– 45 J) – (-31) J • 28 J = (EF – 45 J) + 31 J • -3 J = EF– 45 J • EF= 42 J

44. Practice Problems • The internal energy of a system is initially 165 J. After 20 J of heat is added to the system, the internal energy is measured to be 55 J. How much work was done on the system? • The internal energy of a system is initially 45 J. A total of 20 J of heat energy is added to the system while the system does 10 J of work. What is the system’s final internal energy?

45. Today’s Agenda

46. Exit Slip • 1. _____ is the type of heat transfer that occurs from the sun’s rays. • A. Radiation • B. Conduction • C. Convection • 2. True or false: In conduction, the molecules actually move from one object to another. • 3. An object’s internal energy decreases from 45 J to 35 J when 50 J of work is done. What is the amount of heat energy lost by the system during this?