Thermodynamics

1. Thermodynamics

2. Thermodynamics • Thermodynamics is the study of energy (especially the conversion of energy from one form to another) • Thermodynamics as a science is energy transformation of all forms of energy including living and non-living organisms. Video

3. Thermo Examples

4. Macroscopic Nature of Thermo • Macro means large • We will look at particles at the solid, liquid, and gaseous state.

5. State Variables • The parameters used to describe a macroscopic systems are known as state variables. (they describe the state of the system) • They include: volume, pressure, mass, density, temperature, and specific heat.

6. Changing the State of System • If we change the value of any of the state variables, we are changing the state of the system. What does compressing a gas mean? Thermal Equilibrium indicates that the state variables are constant and not changing.

7. Temperature • Temperature is the quantity that tells you how cold something is compared with a standard • Temperature is related to a system’s thermal energy. • Thermal energy is the kinetic and potential energy of the atoms and molecules in a system as they vibrate (a solid) or move around (a gas)

8. Temperature • Temperature is a measure of the average energy of the particles in a substance. • The faster the particles move, the greater their kinetic energy, and the greater the temperature. Kinetic Energy applet (Kinetic books 28.4)

9. Temperature Scales • A device that measures temperature is a thermometer. Temperature Scales • Celsius – freezing point of water = 0° and the boiling point = 100°. • Kelvin – based on “absolute” temperatures with the same scale as the Celsius scale; must be used in gas laws

10. Kelvin Scale K = C+273 • The lowest temperature possible is called absolute zero. • 0 K = -273.15 °C = -460 °F What is the Kelvin temperature of an object that is 22˚ C?

11. Absolute Zero • Absolute zero is the theoretical temperature at which all kinetic motion is stopped and there are no intra-molecular interactions. Anything at absolute zero has zero volume (which isn’t possible) • Scientists have reached temperatures as low as 2.0 X 10-9 K.

12. Heat (Q) • The energy that transfers form one object to another because of a temperature difference. • Matter does NOT contain heat. • Heat is simply energy in transit from a body of higher temperature to a lower temperature. Heat = Thermal Energy = Internal Energy

13. Heat • Heat is energy transferred from one substance to another by a temperature difference. • Since heat is just energy, the unit is the same (Joule) • The unit of heat is defined as the heat necessary to produce some standard agreed on temperature change for a specified mass of material.

14. Calerie • A calorie is defined as the amount of heat needed to heat 1 gram of water 1°C • The Calorie you know and hate is actually the kilo-calorie (1000 calories = 1 Calorie) 1 cal = 4.184 J

15. James Joule • James Joule was a British physicist who first showed definitively that work could be converted to heat • You can prove the same thing to yourself by vigorously rubbing your hands together on a cold day

16. Temperature vs. Heat • Just because two objects have the same temperature does not mean they both contain the same amount of heat Lead Tree sap T = 75 °C T = 75 °C 3000 J of heat 9000 J of heat

17. Heat and Temperature Are NOT The same! Even though they are at the same temperature (the average kinetic energy of the particles is the same) the sap and lead have different amounts of energy. This is because they are different substances!

18. The temperature of an object depends on: • The substance (what the object is made of) • The mass of the object • The amount of heat energy in the object

19. Specific Heat (c) (Another state function) • When energy flows into a substance, the amount of temperature gain is dependant on the properties of the substance. Not all substances gain heat at the same rate. • The specific heat of a substance is the amount of energy needed to raise a certain amount of a substance one unit of temperature.

20. Specific Heat The symbol for heat gained (or lost) by a substance is ΔQ

21. Specific Heat of Water • Water has one of the highest specific heats known, which goes a long way in determining the properties of life

22. Specific Heat • The higher the specific heat, the more thermal energy is needed to raise the temperature of the object • Thus, an object with a high specific heat will take more heat (and usually a longer time) to heat up and cool off (it has more thermal energy to get rid of)

23. Specific Heat • Absorbed heat can affect substances different ways. • Can increase the translational speed of molecules (increase in temperature) • Can increase the rotation of the molecules , increase the internal vibration within the molecules, or stretch intermolecular bonds (energy stored as potential energy)

24. Specific Heats

25. Trends in Specific Heat • Metals tend to have very low specific heats; they change temperature readily • Liquid water has one of the highest specific heats known, which in general is a very good thing. Why do metals have a low specific heat?

26. Question Which has a higher specific heat…water or sand?

27. Pressure (a state function) • Pressure is defined as Force over Area P = F/A • A gas exerts pressure on its container due to the collisions the atoms make with the walls • The more collisions and the faster the atoms move, the higher the pressure. • The SI Unit for Pressure is the Pascal (Pa)

28. Pressure • Atmospheric Pressure is 1.01 x 105 Pa • As heat is added to a gas sample, the atoms move faster and therefore collide with the walls of the container more often. • This results in an increase in pressure.

29. Pressure • What other ways can the pressure of a gas be changed? Show Kinetic Books Pressure java app

30. Bed of Nails

31. Internal Energy (U) • Internal energy is the grand total of all energies inside of a substance. • The energies include: the jostling molecules, the rotational kinetic energy, kinetic energy of movement of atoms, and potential energy due to the forces between molecules.

32. Internal Energy of Gases • The internal energy of gasses can be calculated according to the following formula U = 3/2 nRT n: number of moles R: Universal gas constant 8.31 J/mol K T: Temperature in Kelvin

33. Calculate Internal Energy Calculate the internal energy of 2 moles of Argon gas at a temperature of 25˚ C.

34. Question A cup of hot tea is poured from a teapot, and a swimming pool if filled with cold water. • Which one has a higher internal energy? • Which has a higher average kinetic energy?

35. Innocent collection of gas molecules, minding their own business If they were to somehow gain energy…

36. We would see that on average, the gas particles are moving faster Now, the individual particles have more energy, so as a whole, the gas has more energy, in the form of heat. We say that the gas has gained internal energy

37. Transfer of Heat

38. When is heat transferred? • Heat is transferred when two objects are in thermal equilibrium and have different temperatures. • The objects continue to transfer heat until they have the same temperature – they are in thermal equilibrium.

39. Transfer of Heat Heat is transferred by three methods: • Conduction • Convection • Radiation

40. Conduction • Conduction is the direct transfer of kinetic energy through collisions. • In any collision, energy is transferred. • Conduction is possible over distances only if all intermediate substances are also heated

41. Cold HOT!!! Heat

42. Conductors • Conductors are materials that conduct heat well (Ex: Metals) • Metals has loosely bound electrons when a metal is heated the molecules vibrate rapidly and the free electrons are able to move through the metal.

43. Insulators • Insulators are poor conductors of heat as they delay the transfer of heat. (Ex: wood, wool, straw, paper) • Liquid and gases are good insulators? Why

44. Question • Why is the snow coverage the same on all roofs?

45. Question • Does a “warm” blanket provide you with heat?

46. Question • Why can you stick your hand into a oven for several seconds without harm, whereas you would never touch the metal inside oven even for a second?

47. Convection • Convection refers to the movement of fluid based on temperature differences. • As the fluid moves, heat is transferred • You all know that warm air rises and cool air descends; thus causing convection

48. Convection • During convection, energy moves from one place to another, but the molecules do not. • Convection occurs in all fluids (liquids and gases)

49. Question • Why can you hold your fingers beside the candle flame without harm, but not above the flame?

50. Radiation • Radiation is the transfer of heat via electromagnetic radiation • A hot body produces radiation, which strikes another body, exciting its particles and therefore generating heat. • Heats indirectly; no direct contact necessary