Chapter 10 Heat

1. Chapter 10 Heat Cadar Revised Shephard

2. Temperature• is the measure of kinetic energy, motion of molecules inside an object. • Temperature is not Heat!! • How hot or cold something “FEELS” ●

3. Adding or removing energy usually changes temperature. (except for during phase changes)

4. If the molecules of a substance are moving slowly, then the temperature of the object is coolerglass of water • If the molecules of a substance are moving very fast, then the temperature will be hotter. pot boiling water LOW KE HIGH KE

5. Temperature Scales Ice point Steam point 0F 320 2120 0C 00 1000 K 273.15 373.15 absolute zero: (no molecular movement)

6. Fahrenheit Scale - used in non-scientific uses in the United States • Celsius Scale – internationally non-scientific meterology, medicine and scientific uses. • Kelvin Scale – physical chemistry, gas laws, astrophysics, and low- temperature physics

7. Temperature Conversions TF = 9 TC + 32 5 TC = 5 (TF - 32) 9 TK = TC + 273.15

8. What are the equivalent Celsius and Kelvin temperatures of 500 F? TC = 10 0C TK = TC + 273.15 TK = 283.15 K TC = 5 (TF - 32) 9

9. Internal Energy • Internal Energy(symbol U) • Isthe total kinetic and potential energy insidean object due to the random individual atomic motions. • Is proportional to a substance’s temperature.

10. The amount of internal energy has to do with the nature of the material, mass of the material, and temperature of the material. • Example: • 100 g hot water has more energy than • 100 g of cold water. • A swimming pool of 10,000 kg of cold • water has more energy than a cup of • hot water because the difference in mass

11. All molecules have 3 types of kinetic motion associated with internal motion. • A molecules potential energy is • due to the bond forces between • atoms.

12. 1) Translational movement forward or backward Kinetic energy atomic motions:

13. 2) Vibrational– small, fast movements back and forth

14. 3) Rotationalmovement – spinning motion

15. Temperature is decided by how much a molecule or atom bounces around a container and hits other molecules and atoms. • Which type of movement is this?

16. Temperature of an object is dependent upon translational movement only.

17. Heat and Energy Ways to increase a substance’s internal energy: • Heat addition • Friction- pulling a nail out of wood, the wood and nail get hot • Deformation- rubber band is stretched, it gets warm; piece of metal bent gets warm

18. Energy transfer depends on temperature differences

19. Heat is energy transferred between objects of different temperatures. • Transfer of heat energy is alwaysfrom the warmer object to the colder object. 850 250

20. Units& Symbols for Heat and Energy • Heat has the units of energy (Joules, J) • Heat is indicated by the symbol Q.

21. Conservation of Energy • Total Energy is conserved. • The change in potential energy + the change in kinetic energy + the change in internal energy = 0 • Conservation of energy equation: PE + ∆KE + ∆U = 0

22. Heat Transfer Equation: Heat (Q) transferred from an object = increase or decrease of internal energy (U). Q = ΔU

23. SPECIFIC HEAT CAPACITY • Every substance has it’s own value for the amount of energy it needs to change the temperature of 1 kg of a substance by 10 C. • This is value is known as specific heat.

24. Specific Heat symbol cp • Units are J/Kg0C

25. Water has a high specific heat. It takes more energy to increase the temperature of water than for any other substance in nature. • Specific heat of water is 4186 J/kg•0 C • A large specific heat number means you have to put a lot of heat energy into a substance for each degree increase in temperature.

26. The value of specific heat indicates how well a substance “holds “heat.

27. HEAT EQUATION specific heat Q = m c ∆ T Heat energy change in (joules mass (g) temperature (0C) or calories)

28. FINDING HEAT: How much heat is needed to raise the temperature of 250 kg of water from 200C to 400C? (specific heat capacity of water 4184J/kg0C )

29. 1. What are you asked to find? 2. Write the given info. 3. Get the formula. 4. Plug in the numbers

30. FINDING HEAT Unknown - heat Q Mass - 250kg Δ T - 200C C - 4186J/kg0C Q = mc∆T Q = (250kg) x (4186J/kg0C) x 200C) Q = 2.1 x 107J

31. CALORIMETRY • Using the specific heat of water known to be 4186 J/Kg0C, we can use an approach called calorimetry to determine a 2nd object’s specific heat.

32. We place a heated unknown object in an insulated container of cool water.

33. Since energy is conserved, the energy the substance gives up must equal the energy absorbed by the water.

34. Calorimetry Equation • cp,wmw∆Tw = cp,xmx∆Tx • Specific heat of waterxmass of water x change in temperature of water = specific heat of unknown x mass of unknown x change in temperature of uknown

35. PHASE CHANGE • Phase changes involve potential energy between particles. • Potential energy is present among a collection of particles in a solid or a liquid in the form of attractive bonds.

36. The potential energy increases with increasing atomic separation from the equilibrium position. This resembles a spring. • If the particles are far enough apart, the bonds between them break and release kinetic energy.

37. LATENT HEAT • Latent heat is the energy per unit mass that is transferred during a phase change of a substance. • Units of Latent Heat = J/Kg • Latent Heat Equation Q = mLlatent heat heat transferred as heat during mass phase change

38. Thermal Equilibrium • is the state in which two bodies in physical contact with each other have identical temperatures.

39. THERMAL EXPANSION Most materials expand when heated due to increased molecular motion. Liquid in a thermometer rises with heat Running hot water on a jar lid expands the metal and loosens the lid.

40. Each material has its own coefficient of expansion - gasses have the largest values. - solids have smallest values

41. Liquids tend to expand with increasing temperatures • Water increases volume with temperature except between 40to 00C where water increases volume with decreasing temperature

42. This behavior or water is due to its open angular crystal structure and stronger binding forces at certain angles. • Consequently, ice has a greater volume than its liquid state. • Ice is LESS DENSE than water and therefore floats on top of water.

43. Examples: Expansion joints in bridges Concrete Jar lids

44. THERMAL CONDUCTION • Energy transferred as Heat between two points of different temperatures in contact with each other.

45. THERMAL CONDUCTION As an object is heated, the atoms nearest the heat vibrate with greater energy. These vibrating atoms jostle their less energetic neighbors and transfer some of their energy. Gradually, atoms farther away from the heat are also vibrated and gain energy.

46. THERMAL CONDUCTION More specifically, it is the free electrons of the vibrating heated atoms that drift through the material transferring energy by colliding with atoms and other free electron within the material.

47. THERMAL CONDUCTION CONT’D Metals are the best conductors of HEAT and ELECTRICITY because they have the “loosest” outer electrons, than other materials.

48. CONVECTION • Convection involves the displacement of cold matter by hotter matter, such as when hot air over a flame rises upward. • Occurs in Gasses & liquids that flow as currents.

49. CONVECTION CONT’D This method does not use heat alone but uses pressure and buoyancy also.

50. Wind Convection Currents • Convection currents stir in the atmosphere to produce winds. • The land at the shore absorbs the sun’s heat more readily than the Sea since water has a higher specific heat value. • Air above the shore rises as cooler air from above the water takes its place. • At nighttime the reverse happens