Chapter 10

1. Chapter 10 Heat Cadar Revised Shephard

2. TEMPERATUREis the measure of kinetic energy of molecules inside an object. • Changes in temperature are proportional to changes in kinetic energy of molecules

3. Temperature Scales Ice point Steam point Fahrenheit320 F 2120 F Celcius00 C1000 C Kelvin - 273 K 373 K

4. Temperature Scales and Uses Fahrenheitnon scientific uses meteorology, medicine Celsius meterology, medicine and other sciences internationally Kelvin physical chemistry, gas laws astrophysics, thermodynamics low temperature physics

5. Temperature Equations • TF = 9 TC + 32 5 • TC = 5 TF – 32 9 • K = TC + 273.15

6. TEMPERATURE CALCULATE THE FOLLOWING CONVERSIONS CONVERT 250C TO FAHRENHEIT CONVERT 1250C TO KELVIN CONVERT 3250F TO CELSIUS K is absolute zero, no molecular movement 770F 398.15 K 162.780C

7. TEMPERATURE • 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

8. Internal Energy • Internal energy (symbol U) is the total energy inside an object due to the random kinetic energy motions of its individual molecules and potential energy due to forces between molecules.

9. Internal Energy& Temperature Internal energy is proportional to a substance’s temperature.

10. Internal Energy& Temperature All molecules have 3 types of kinetic motion associated with internal motion

11. 1) Translational movement – forward or backward movement Internal Energy& Temperature

12. Internal Energy& Temperature 3) Vibration – small, fast movements back and forth

13. Internal Energy& Temperature 2) Rotational movement – spinning motion

14. Internal Energy & Temperature 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?

15. Translational

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

17. Heat and Energy WAYS TO INCREASE A SUBSTANCE’S INTERNAL ENERGY: • 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. Heat and Energy Energy that is transferred between objects of different temperatures is defined as heat.

19. Heat and Energy Energy transfer depends on temperature difference

20. Heat and Energy Transfer of heat energy is always from the warmer object to the colder object.

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

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

23. Conservation of Energy • Heat (Q) transferred from an object = increase or decrease of internal energy (U). • Q = ΔU

24. SPECIFIC HEAT CAPACITY • Each 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.

25. Specific Heat continued • Water has a high specific heat • Specific heat of water is 1.00 calorie gram 0C • It takes more energy to increase the temperature of water than for other substances in nature. • Every substance has a different specific heat.

26. Specific Heat continued A large specific heat number means you have to put a lot of heat energy into a substance for each degree increase in temperature.

27. Specific Heat Equation • Specific Heat = energy transferred as heat / (mass x change in temperature) • cp = Q / (m ∆T)

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

29. SPECIFIC HEAT • Specific Heat = cp • Units are J/Kg0C

30. FINDING HEAT: How much heat is needed to raise the temperature of 250 g of water from 200C to 400C? (specific heat capacity of water = 1cal/g0C or 4184J/kg0C

31. FINDING HEAT • What are you asked to find? • Write the given info. 3. Get the formula. 4. Plug in the numbers

32. FINDING HEAT Unknown - heat Q Mass - 250g Δ T - 200C C - 1cal/g0C Q = mc∆T Q = (250g) x (1calorie/g0C) x (200C) Q = 5,000 calories Use the conversion factor 4.184 J/cal to convert calories to joules.

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

34. CALORIMETRY • We place a heated unknown object in an insulated container of cool water.

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

36. CALORIMETRY EQUATION • 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 • cp,wmw∆Tw = cp,xmx∆Tx

37. PHASE CHANGE PHASE CHANGE PHASE CHANGE

38. 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.

39. PHASE CHANGE • 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.

40. 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 • Energy transferred as heat during a phase change = mass x latent heat • Q = mL

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

42. 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.

43. THERMAL EXPANSION • Each material has its own coefficient of expansion - gasses have the largest values. - solids have smallest values

44. THERMAL EXPANSION • Liquids tend to expand with increasing temperatures • Water increases volume with temperature except at 00 to - 40 water increases volume with decreasing temperature

45. THERMAL EXPANSION Examples: Expansion joints in bridges, concrete Jar lids Ice expands from 00 – 40C

46. THERMODYNAMICS The study of how heat moves Heat transfers from hot to cold 250C 50C Heat does not rise (hot air rises)

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

48. 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.

49. 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.

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