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Thermodynamics lecture 2

A
Archit Gadhok

The document discusses key concepts in thermodynamics including: 1) Thermal equilibrium occurs when two systems in contact across a thermal conductor reach the same temperature. 2) A pure substance's phase behavior is characterized by its temperature-volume diagram, with liquid-vapor coexistence occurring along the saturation curve. 3) A substance's vapor pressure increases uniquely with temperature and defines its boiling point at given pressures, terminating at the critical point where liquid and vapor can no longer be distinguished.

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BITS Pil i Pilani Pilani Campus Lecture 2: P L t 2 Processes; Th Thermal equilibrium and l ilib i d Temperature; Phase behavior of pure substance
State Postulate Phase Spatially uniform (in chemical composition and physical properties), mechanically separable part of system Homogeneous single phase, else heterogeneous Pure substance one of unvarying chemical constitution Simple, compressible substance only form of work that of volume change, no magnetic, electrical, effects etc., Also we will normally ignore surface effects Postulate two intensive properties suffice to determine all others (ie., determine the equilibrium state) of a single phase, pure simple compressible substance. If i addition, h i l ibl b t If, in dditi the mass is known then so are all other extensive properties Also applies to a mixture of fixed composition such as air in a single phase BITSPilani, Pilani Campus
Equilibrium surface Properties are also called state functions Set of all equilibrium states constitutes a surface in the space of independent intensive variables BITSPilani, Pilani Campus
Process Process system goes from state i to state f. In so doing, in general it will interact with the surroundings Quasistatic process intervening states are all equilibrium states slow and controlled Isobaric isochoric, isothermal processes Isobaric, isochoric If intervening states not equilibrium states, then shown dashed Cycle Initial and final states are the same BITSPilani, Pilani Campus
Thermal Equilibrium Diathermal material One which allows two systems in contact across a rigid wall of such a material to influence g each others state, eg., copper. (It is a thermal conductor) Adiabatic material One which does not permit such an interaction as above when in the form of a rigid wall separating two systems, ie., it is a thermal insulator S t Systems separated by a di th t db diathermal wall are i th l ll in thermal l contact, and will reach thermal equilibrium Zeroth Law of Thermodynamics If A and B are separately in thermal equilibrium with C, then A and B will be in thermal equilibrium with one another An experiment with gases equation of state BITSPilani, Pilani Campus
Temperature and Thermometry States in thermal equilibrium with one another have the same temperature T Equation of state: A relationship between P, v, and T, characteristic of a substance T can be used as one of the variables t characterize th b d f th i bl to h t i the state, ie., v= v(P,T) Thermometry: Such a relationship that enables one to determine the temperature from a measurement of a property for eg., height of mercury in capillary, resistance of a wire pressure of a fixed volume of a gas wire, T also determines as we all know the direction in which heat transfer occurs, though we will introduce the concept of g p heat formally a little later in this course. BITSPilani, Pilani Campus
Pressure Pressure:Normalforceexertedbyafluidperunitarea P = 隆Fn/隆A SIunit1Pascal(Pa)=1N/m2 1bar=105 Pa=0.1MPa=100kPa 1 bar = 105Pa = 0 1MPa = 100kPa 1atm =101325Pa=101.325kPa 1Torr =1mmofHg=133.3224Pa g Absolute Pressure and Gauge Pressure Hydrostatic Pressure due to a column of fluid of height h in gravitational field P = gh is the pressure difference g p BITSPilani, Pilani Campus
際際滷 headings here Barometermeasuring Manometermeasuringpressure p absolutepressure relativetoatmosphericpressure p p BITSPilani, Pilani Campus
Scales of Temperature Gas thermometer ideal gas scale T = 273.16(P/Ptp) Celsius Ttp = 0.01尊 C, ice point = 0尊C, steam point = 100.0 尊CC Kelvin = 尊C + 273.15 (Absolute), Coincides with the ideal gas scale BITSPilani, Pilani Campus
Pure Substance Phase Behavior Experiment with water at Constant Pressure: T-v behavior Saturation Temperature temperature at which liquid and vapor coexist at given P, ie., the boiling temperature Saturation Pressure pressure at which liquid and vapor coexist at given Y i th vapor pressure i Y, ie., the The saturation T of water at 0.1 MPa is 99.6尊 C, and vice versa At fixed pressure, the temperature does not change as long as the two phases coexist If heat is added the relative amount of vapor increases coexist. added, BITSPilani, Pilani Campus
Vapor Pressure The vapor pressure of a pure liquid increases with increasing temperature The vapor pressure has a unique value at a given temperature The vapor pressure curve terminates at a critical point beyond which there is no distinction between liquid and vapor BITSPilani, Pilani Campus
T-v diagram for water BITSPilani, Pilani Campus

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Thermodynamics lecture 2

  • 1. BITS Pil i Pilani Pilani Campus Lecture 2: P L t 2 Processes; Th Thermal equilibrium and l ilib i d Temperature; Phase behavior of pure substance
  • 2. State Postulate Phase Spatially uniform (in chemical composition and physical properties), mechanically separable part of system Homogeneous single phase, else heterogeneous Pure substance one of unvarying chemical constitution Simple, compressible substance only form of work that of volume change, no magnetic, electrical, effects etc., Also we will normally ignore surface effects Postulate two intensive properties suffice to determine all others (ie., determine the equilibrium state) of a single phase, pure simple compressible substance. If i addition, h i l ibl b t If, in dditi the mass is known then so are all other extensive properties Also applies to a mixture of fixed composition such as air in a single phase BITSPilani, Pilani Campus
  • 3. Equilibrium surface Properties are also called state functions Set of all equilibrium states constitutes a surface in the space of independent intensive variables BITSPilani, Pilani Campus
  • 4. Process Process system goes from state i to state f. In so doing, in general it will interact with the surroundings Quasistatic process intervening states are all equilibrium states slow and controlled Isobaric isochoric, isothermal processes Isobaric, isochoric If intervening states not equilibrium states, then shown dashed Cycle Initial and final states are the same BITSPilani, Pilani Campus
  • 5. Thermal Equilibrium Diathermal material One which allows two systems in contact across a rigid wall of such a material to influence g each others state, eg., copper. (It is a thermal conductor) Adiabatic material One which does not permit such an interaction as above when in the form of a rigid wall separating two systems, ie., it is a thermal insulator S t Systems separated by a di th t db diathermal wall are i th l ll in thermal l contact, and will reach thermal equilibrium Zeroth Law of Thermodynamics If A and B are separately in thermal equilibrium with C, then A and B will be in thermal equilibrium with one another An experiment with gases equation of state BITSPilani, Pilani Campus
  • 6. Temperature and Thermometry States in thermal equilibrium with one another have the same temperature T Equation of state: A relationship between P, v, and T, characteristic of a substance T can be used as one of the variables t characterize th b d f th i bl to h t i the state, ie., v= v(P,T) Thermometry: Such a relationship that enables one to determine the temperature from a measurement of a property for eg., height of mercury in capillary, resistance of a wire pressure of a fixed volume of a gas wire, T also determines as we all know the direction in which heat transfer occurs, though we will introduce the concept of g p heat formally a little later in this course. BITSPilani, Pilani Campus
  • 7. Pressure Pressure:Normalforceexertedbyafluidperunitarea P = 隆Fn/隆A SIunit1Pascal(Pa)=1N/m2 1bar=105 Pa=0.1MPa=100kPa 1 bar = 105Pa = 0 1MPa = 100kPa 1atm =101325Pa=101.325kPa 1Torr =1mmofHg=133.3224Pa g Absolute Pressure and Gauge Pressure Hydrostatic Pressure due to a column of fluid of height h in gravitational field P = gh is the pressure difference g p BITSPilani, Pilani Campus
  • 8. 際際滷 headings here Barometermeasuring Manometermeasuringpressure p absolutepressure relativetoatmosphericpressure p p BITSPilani, Pilani Campus
  • 9. Scales of Temperature Gas thermometer ideal gas scale T = 273.16(P/Ptp) Celsius Ttp = 0.01尊 C, ice point = 0尊C, steam point = 100.0 尊CC Kelvin = 尊C + 273.15 (Absolute), Coincides with the ideal gas scale BITSPilani, Pilani Campus
  • 10. Pure Substance Phase Behavior Experiment with water at Constant Pressure: T-v behavior Saturation Temperature temperature at which liquid and vapor coexist at given P, ie., the boiling temperature Saturation Pressure pressure at which liquid and vapor coexist at given Y i th vapor pressure i Y, ie., the The saturation T of water at 0.1 MPa is 99.6尊 C, and vice versa At fixed pressure, the temperature does not change as long as the two phases coexist If heat is added the relative amount of vapor increases coexist. added, BITSPilani, Pilani Campus
  • 11. Vapor Pressure The vapor pressure of a pure liquid increases with increasing temperature The vapor pressure has a unique value at a given temperature The vapor pressure curve terminates at a critical point beyond which there is no distinction between liquid and vapor BITSPilani, Pilani Campus
  • 12. T-v diagram for water BITSPilani, Pilani Campus