17 Section 2 Notes: Kinetic Energy and Temperature Kinetic energy (KE)- Energy of movementTemperature- A measure proportional to the average kinetic energy of a substance.higher temperature = higher kinetic energyThe more kinetic energy the quicker the molecules are moving around
19 Draw a picture representing molecular motion of three identical molecules at these two temperatures
20 Draw a picture representing molecular motion of three identical molecules at these two temperatures
21 Internal Energy vs. Heat Section 3 Notes:Internal Energy vs. HeatInternal energy (U)- Sum of the molecular energykinetic energy, potential energy, and all other energies in the molecules of a substance.Unit: JouleHeat (Q) is energy in transitenergy flows from a hot to a cold substance.An object never has “heat” or “work” only internal energy (heat is transferred and work is done)
22 Heat is energy in transit Heat lost by one object equals heat gained by anotherHeat lost = Heat gained-QA = QB
23 Heat transfers from hot to cold Holding a hot cupHoling a cold glass (heat leaving your hand feels cold)
24 Example 3The coffee looses 468J of heat. How much heat does Bob gain? (assuming no heat was lost to the surroundings)The same: Bob gained 468 J of heat
25 Direction: From high temperature to low temperature Rate of transfer depends on temperature difference: The greater temperature difference the greater the energy transferTwater =20º CTcan =15º CTwater =35º CTcan =5º C
27 Example 4Where would the greater energy transfer take place and which way would the energy transfer?Ice = 0 ºC Juice = 20 ºCIce = 0 ºC Juice = 25 ºCB. has a bigger temperature difference and therefore greater energy transfer.Energy transfers from hot to cold: Juice to Ice
28 What happens when the temperature inside and out are equal? Twater =11º CTcan =
29 Heat is transferred until there is thermal equilibrium Thermal Equilibrium- When temperatures are equal and there is an even exchange of heatTwater =11º CTcan =
30 Section 4 Notes: Heat Transfer Types of Heat Transfer:ConductionConvectionRadiation
31 Conduction- Caused by vibrating molecules transferring their energy to nearby molecules. Not an actual flow of molecules.heat transfer
32 Thermal conductors- rapidly transfer energy as heat Thermal insulators- slowly transfer energy as heat
33 ChallengePut the following in order of most thermally conductive to least.Copper, Wood, Air, Water, Concrete12345
35 Convection- process in which heat is carried from place to place by the bulk movement of a fluid (gas or liquid).Examples
36 Radiation (electromagnetic radiation) – Reduce internal energy by giving off electromagnetic radiation of particular wavelengths or heated by an absorption of wavelengths.Ex. The UV radiation from thesun making something hot. Absorptiondepends on the material.
37 Draw your own pictures in the table that represent these three types of heat transfer.
38 Draw your own pictures in the table that represent these three types of heat transfer.
40 A SystemSystem- A collection of objects upon which attention is being focused on.This system includes the flask, water and steam, balloon, and flame.Surroundings- everything elsein the environmentThe system and surrounding areseparated by walls of some kind.SystemSurroundings
41 Walls between a system and the outside Adiabatic walls- perfectly insulating walls. No heat flow between system and surroundings.
42 In a system: How can you measure the quantity of heat entering or leaving? Q = Δ U or Q = Uf – U0Q: The quantity of heat that enters or leaves a systemU0: Initial internal energy in systemUf: Final internal energy in systemIf Q is positive then energy entered the systemIf Q is negative then energy left the systemThis is directly related to temperature.If the system gets colder then heat leftIf the system gets warmer then heat entered
43 Example 5 The internal energy of the substance is 50 J before The internal energy of the substance is 145 J aftera) How much heat was transferred in this system?b) Did it enter or leave?
44 ΔU = Q + W First Law of Thermodynamics: Conservation of energy applied to thermal systems.Energy can neither be created nor destroyed. It can only change formsStated in an equationΔU = Q + W
45 First Law of Thermodynamics: Conservation of Energy ΔU = Q + WInternal Energy (U)(positive if internal energy is gained)Heat (Q)(positive if heat is transferred in)Work (W)(positive if work is done on the system)The unit for all of these is the Joule (J)
46 Example 6 & 76. A system gains 1500 J of heat from its surroundings, and 2200 J of work is done by the system on the surroundings. What is the change in internal energy?7. A system gains of heat, but 2200 J of work is done on the system by the surroundings. What is the change in internal energy?
47 Example 6 & 76. A system gains 1500 J of heat from its surroundings, and 2200 J of work is done by the system on the surroundings. What is the change in internal energy?7. A system gains of heat, but 2200 J of work is done on the system by the surroundings. What is the change in internal energy?
48 Now how can you tell if work is done by or on a system? Is work done on or by the system ?nail/wood system b) Bunsen burner,flask, balloon system
49 Work done on a system: Work to Internal Energy Work is done by the man causing frictional forces between the nail and the wood fiber.Work increases the internal energy of the wood and nail.
50 Work done by a system: Internal Energy to Work The balloon expands doing work on its surroundingsThe expanding balloon pushes the air away
51 Work done on or by a gas Volume must change or no work is done. On a gas- Volume decreases (work must be done to force molecules into a smaller area)By a gas- Volume increases (the pressure of the gas causes the volume to increase)
52 Section 5 Notes 4 Common Thermal Processes Isobaric Process Isochoric process (isovolumetric)Isothermal processAdiabatic processEach will have their own assumptions
53 4 Thermal Processes Isobaric Process – occurs at constant pressure
54 4 Thermal ProcessesIsochoric process (Isovolumetric) – one that occurs at constant volume.ΔV = 0 and therefore W = 0
55 Thermal ProcessesIsothermal process – one that occurs at constant temperatureT (temperature) directly relates to U (internal energy)ΔU = 0
56 Thermal ProcessesAdiabatic process – on that occurs with no transfer of heatΔQ = 0
57 Example 8How much heat has entered or left the system when 500J of work has been done on the system in an isothermal process?
58 Example 8How much heat has entered or left the system when 500J of work has been done on the system in an isothermal process?
59 Example 9How much work is done on or by the system when internal energy increases by 55J in n adiabatic process?
60 Example 9How much work is done on or by the system when internal energy increases by 55J in n adiabatic process?
62 First Law of Thermodynamics Energy Conservation: Conservation of energy applied to thermal systems.Energy can neither be created nor destroyed. It can only change formsWhen heat is added to a system, it transforms to an equal amount of some other form of energy.Equation:ΔU = Q + W (work is done on a system)
63 Second Law of Thermodynamics (Second Law) Law of EntropyHeat goes from hot to cold.No cyclic process is 100% efficientit can’t convert heat entirely into workSome energy will always be transferred out to surroundings as heat.Energy systems have a tendency to increase their entropy or disorder.Entropy- Measure of randomness or disorder in a system
64 Third Law of Thermodynamics As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.A theoretical impossibilityIf it occurred everything would stop and there would be no more entropy
65 Section 7: Transformation of energy in a heat engine
66 The Heat Enginea device that used a difference in temperature of two substances to do mechanical workIt transferring energy from a high-temperature substance (the boiler) to a lower temperature substanceFor each complete cycle: Wnet = Qh - QcWhat the variables stand for here:Qh = Heat from high temperature substanceQc = Heat to low temperature substanceW or work equals the difference of Qh and Qc
67 The Heat Engine How it works: main points There will be an area of high temperature (boiler) and an area of low temperatureHeat wants to go from a high temperature to a low temperature.Work is done by capturing energy in the transfer and using it to do workThe work done by the engine equals the difference in heat transferred from the hot to cold substance.
68 The Heat EngineFor each complete cycle: Work = Energy transferred as heat from the high temperature substance to the colder temperature substanceWhat the variables stand for here:Qh = Heat from high temperature substanceQc = Heat to low temperature substanceW or work equals the difference of Qh and Qc
69 Example 10A heat engine is working at 50% efficiency. How much work is done between a 670J and 200J reservoir?
70 Example 10A heat engine is working at 50% efficiency. How much work is done between a 670J and 200J reservoir?