by prof.xiangyang liu biophysics & micro/nanostructures
TRANSCRIPT
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Why is thermodynamics important?
ll l h l dAll light related processes should obey thermodynamics laws!laws!
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Thermodynamic states.Thermodynamic properties/state functionsThermodynamic properties/state functions, extensive/intensive properties. E, H, SPhase diagramgZeroth Law of ThermodynamicsFirst law of thermodynamicsThermal Processes
isobaric: constant pressurei h i t t lisochoric: constant volumeisothermal: constant temperatureadiabatic: no transfer of heatadiabatic: no transfer of heat
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Thermodynamic Systems andThermodynamic Systems and Their Surroundings
h d i h b h f hThermodynamics is the branch of physics that is built upon the fundamental laws that heat and work obey.The collection of objects on which attention is The collection of objects on which attention is being focused is called the system, while everything else in the environment is called the surroundings.Walls that permit heat flow are called diathermal walls, while walls that do not permit heat flow are called adiabatic walls.T d t d th d i it i To understand thermodynamics, it is necessary to describe the state of a system.
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Thermodynamic (state) properties
Extensive properties: the quantity isproportional to the amount of all
b t V M U tsubstances: V, M, U, etc.Intensive properties: the quantitydepends only on the relative amountsdepends only on the relative amountsof different substances: ρ, T, P, C, etc.
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Thermodynamic states
A certain number of variables (state propertiesor functions), ie. T,P,M, will specify the state ofor functions), ie. T,P,M, will specify the state ofthe system. f(P,V,M,x1, x2, x3, …)‐ state equation.Thermodynamic equilibrium state: A defined y qstate of a system is in equilibrium when the values of its state variables are independent of time.
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The Zeroth Law ofThe Zeroth Law of Thermodynamics
Two systems are said to be in thermal equilibrium if there is no heat flow between then when o eat o bet ee t e ethey are brought into contact. Temperature is the indicator of thermal equilibrium in the sense thermal equilibrium in the sense that there is no net flow of heat between two systems in thermal contact that have the same contact that have the same temperature.
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The Zeroth Law ofThe Zeroth Law of Thermodynamics
Two systems individually in thermal equilibrium with a third system are in thermal equilibrium with each other.
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Thermodynamic states(Equilibrium) Thermodynamics is concerned with (Equilibrium) Thermodynamics is concerned with changes between equilibrium statesReversible change: ◦ A succession of near‐equilibrium states from initial to final state.
◦ The direction of change can be reversed by an g yinfinitesimal change in the surroundings.
◦ ie. the boiling of water and the condensation of stream at 100C.at 100C.
Irreversible change: All other processes.
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Phase diagramTo specify the thermodynamic equilibrium states in a 2D or 3D diagram
phase diagram for water
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Heat, Work and EnergyHead, q: Energy transferred into and out transferred into and out of a system as a consequence of a temperature difference b h d between the system and its surroundingsWork, w: Any other exchange of energy exchange of energy between the system and its surroundings, ie. volume change against int P surface tension
Electron-high electric potential
Electron-low electric potential int P, surface tension
work, electric work, etc.energy energy
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Internal energy a function of the state of a
Heat, Work and Energy
Internal energy – a function of the state of a system: The energy within the system.◦ Those kinds of energy that might be modified by chemical processes.chemical processes.Translational energyVibrational/rotational energyRotational energygyChemical BondingNon‐bonding interactions between molecules
◦ The energy in holding together the atomic nuclei (nuclear energy) is generally not counted(nuclear energy) is generally not counted.
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Where does energy come from?
Solar energy‐nuclear fusionCh i l Chemical energy stored in covalent bondsbonds
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Bioenergetics: Energy required to maintain life andBioenergetics: Energy required to maintain life and life activities…
To maintain the cellular transport, to
t generate biosignals…Maintain orderMaintain order
Sodium-potassium pumpSodium potassium pump
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The First Law of Thermodynamics
Suppose that a system gains heat Q and that is the only effect occurring.
QUUU if =−=Δoccu g.Consistent with the law of conservation of energy, the internal energy of the system internal energy of the system changes:Heat is positive when the system
i h t d ti h th gains heat and negative when the system loses heat.
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Th Fi L f Th d iThe First Law of Thermodynamics
If t d k W it di d If a system does work W on its surroundings and there is no heat flow, conservation of energy indicates that the internal energy of the system indicates that the internal energy of the system will decrease:
WUUUΔ
Work is positive when it is done by the system and
WUUU if −=−=Δ
Work is positive when it is done by the system and negative when it is done on the system.
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The First Law of Thermodynamics
h l f h dThe internal energy of a system changes due to heat and work:
h h h d
WQUUU if −=−=Δ
Heat is positive when the system gains heat and negative when the system loses heat. W k i i i h i i d b h d Work is positive when it is done by the system and negative when it is done on the system.
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The First Law of Thermodynamics
Example 1 Positive and Negative Work
In part a of figure, the system gains 1500J of heat d J f k i d b th t it and 2200J of work is done by the system on its
surroundings. In part b, the system also gains 1500J of heat, but 2200J of work is done on the system.yIn each case, determine the change in internal energy of the system.
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The First Law of Thermodynamics
Example 2 An Ideal GasThe temperature of three moles of a
i id l i d d f K monatomic ideal gas is reduced from 540K to 350K as 5500J of heat flows into the gas.Find (a) the change in internal energy and (b) Find (a) the change in internal energy and (b) the work done by the gas.
nRTU 23=WQUUU if −=−=Δ
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Thermal ProcessesA quasi‐static process is one that occurs slowly A quasi static process is one that occurs slowly enough that a uniform temperature and pressure exist throughout all regions of the system at all times.
isobaric: constant pressureisobaric: constant pressureisochoric: constant volumeisothermal: constant temperaturedi b ti t f f h tadiabatic: no transfer of heat
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Thermal Processes
An isobaric process is one that occurs at constant An isobaric process is one that occurs at constant pressure.
( ) VPAsPFsW Δ===
Isobaric process:
( )VVPVPW Δ ( )if VVPVPW −=Δ=
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Thermal Processes
Example 3 Isobaric Expansion of Water
One gram of water is placed in the cylinder and the pressure is maintained at 2.0x105Pa. The temperature of the water is raised by 31oC. The water is in the liquid phase and expands by the small amount of 1 0x10‐8m31.0x10 8m3.Find the work done and the change in internal energy.
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Thermal ProcessesThermal Processes
Example 4 Work and the Area U d P V l G hUnder a Pressure‐Volume GraphDetermine the work for the process in which the pressure, volume, and which the pressure, volume, and temperature of a gas are changed along the straight line in the figure.
Th d lThe area under a pressure-volume graph is the work for any kind of process.
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K CKey Concepts
Environment‐systemThermodynamic states‐state functions‐equilibrium‐phase diagramEnergy‐work‐heatIsobaric, isochoric, isothermal, adiabatic processes and the calculations of energy‐work‐hheat