3 Sadi Carnot1796 – 1832French EngineerFounder of the science of thermodynamicsFirst to recognize the relationship between work and heat
4 Thermodynamics is the study of processes in which energy is transferred as heat and as work. IThe internal energy is the sum of all the energy of all the molecules in an object:· random translational kinetic energy· rotational kinetic energy· vibrational energy· intermolecular energy associated with their bonding.
5 ZEROTH LAWThe Zeroth law states that "If bodies A and B are each separately in thermal equilibrium with body C, then A and B are in thermal equilibrium with each other."The common property between A and B is called temperature.
6 1) The First Law of Thermodynamics Topics1) The First Law of Thermodynamics2) Work Done on a Gas3) Pressure - Volume Graph4) Thermodynamic Processes5) The Second Law of Thermodynamics6) Heat Engines7) Carnot cycle8) EntropyThe Laws of Thermodynamics (02 of 38)
7 First Law of Thermodynamics SystemUQWEnvironmentDU = Q - WThe Laws of Thermodynamics (03 of 38)
8 The Ideal Gas Law PV = NkT Volume (m3) Pressure (Pa) Absolute Temperature(K)Number ofMoleculesBoltzmann’sConstant(1.38 x J/K)Temperature and kinetic Theory13
9 Thermodynamic Processes Isobaric Constant PressureIso-volumetric Constant VolumeIsothermal Constant Temp.Adiabatic No Heat Transferbetween systemsThe Laws of Thermodynamics (06 of 38)
10 Pressure - Volume Graph T4T3Isotherms(lines of constanttemperature)T2PT1Area under curve represents workPressureInternal energyis proportionalto temperatureVolumeVThe Laws of Thermodynamics (05 of 38)
11 HEAT ENGINES Qhot Wout Qcold A heat engine is any device which through a cyclic process:Cold Res. TCEngineHot Res. THQhotWoutQcoldAbsorbs heat QhotPerforms work WoutRejects heat Qcold
12 THE SECOND LAW OF THERMODYNAMICS WoutCold Res. TCEngineHot Res. THQhotQcoldIt is impossible to construct an engine that, operating in a cycle, produces no effect other than the extraction of heat from a reservoir and the performance of an equivalent amount of work.Not only can you not win (1st law); you can’t even break even (2nd law)!
13 THE SECOND LAW OF THERMODYNAMICS Cold Res. TCEngineHot Res. TH400 J300 J100 JA possible engine.An IMPOSSIBLE engine.Cold Res. TCEngineHot Res. TH400 J
14 EFFICIENCY OF AN ENGINE The efficiency of a heat engine is the ratio of the net work done W to the heat input QH.Cold Res. TCEngineHot Res. THQHWQCe = =WQHQH - QCe = 1 -QCQH
15 EFFICIENCY EXAMPLE 800 J W 600 J An engine absorbs 800 J and wastes 600 J every cycle. What is the efficiency?Cold Res. TCEngineHot Res. TH800 JW600 Je = 1 -QC-----QHe = 1 -600 J800 Je = 25%Question: How many joules of work is done?
16 EFFICIENCY OF AN IDEAL ENGINE (Carnot Engine) Cold Res. TCEngineHot Res. THQHWQCmaember perfect engine, the quantities Q of heat gained and lost are proportional to the absolute temperatures T.e =TH - TCTHe = 1 -TCTH
17 Work done by engine each cycle The Carnot CycleTh= 550 KTcEngineQhQcW= 470 J= 890 JFor the engineWork done by engine each cycleThe efficiency of the engineThe Laws of Thermodynamics (26 of 38)
18 Temperature of the cool reservoir Engine W = 420 J The Carnot CycleTh= 550 KQh= 890 JTemperature of the cool reservoirEngineW = 420 JQc= 470 JTcThe engine undergoes 22 cycles per second,its mechanical power outputThe Laws of Thermodynamics (27 of 38)
19 A carnot engine absorbs 900 J of heat each cycle and provides 350 J The Carnot CycleThA carnot engine absorbs 900 J ofheat each cycle and provides 350 Jof workQh= 900 JEngineW = 350 JThe efficiency of the engineQcTcThe heat ejected each cycleThe Laws of Thermodynamics (28 of 38)
20 A carnot engine absorbs 900 J of heat each cycle and provides 350 J The Carnot CycleThA carnot engine absorbs 900 J ofheat each cycle and provides 350 Jof workQh= 900 JEngineW = 350 JThe engine ejects heat at 10 oCThe temperature of the hot reservoirQc=550 JTc = 283 KThe Laws of Thermodynamics (29 of 38)
21 The Carnot CycleTh= 650 KTc= 300 KEngineQhQcW = ?= 400 JA carnot engine operates between a hot reservoir at 650 K and a cold reservoir at 300 K. If it absorbs 400 J of heat at the hot reservoir, how much work does it deliver?The Laws of Thermodynamics (30 of 38)
22 Natural processes tend to move toward a state of greater disorder. EntropyEntropy is a measure of the disorder of a system. This gives us yet another statement of the second law:Natural processes tend to move towarda state of greater disorder.Example: If you put milk and sugar in your coffee and stir it, you wind up with coffee that is uniformly milky and sweet.No amount of stirring will get the milk and sugar to come back out of solution.The Laws of Thermodynamics (33 of 38)
23 Thermal equilibrium is a similar process – EntropyAnother example: when a tornado hits a building, there is major damage.You never see a tornado approach a pile of rubble and leave a building behind when it passes.Thermal equilibrium is a similar process –the uniform final state has more disorder than the separate temperatures in the initial state.The Laws of Thermodynamics (34 of 38)
24 Another consequence of the second law: EntropyAnother consequence of the second law:In any natural process, some energybecomes unavailable to do useful work.If we look at the universe as a whole, it seems inevitable that, as more and more energy is converted to unavailable forms, the ability to do work anywhere will gradually vanish. This is called the heat death of the universe.The Laws of Thermodynamics (35 of 38)
25 First law of thermodynamics: SummaryFirst law of thermodynamics:Isothermal process: temperature is constant.Adiabatic process: no heat is exchanged.Work done by gas at constant pressure:Heat engine changes heat into useful work (requires temperature difference).Efficiency of a heat engine:Carnot efficiency:The Laws of Thermodynamics (36 of 38)