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Thermodynamics

Thermodynamics. RAT 11. Class Objectives. Be able to define: thermodynamics temperature, pressure, density, equilibrium, amount of substance states of matter and define them in the context of a phase diagram gas laws. Thermodynamics. Thermodynamics: “Therme” meaning heat, and

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Thermodynamics

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  1. Thermodynamics

  2. RAT 11

  3. Class Objectives • Be able to define: • thermodynamics • temperature, pressure, density, equilibrium, amount of substance • states of matter and define them in the context of a phase diagram • gas laws

  4. Thermodynamics • Thermodynamics: “Therme” meaning heat, and “Dynamics” meaning strength • Thermodynamics is the science of what is possible and impossible • Major limitation: Cannot predict how long the process takes (This is the subject of rate processes)

  5. High T Low T Thermodynamic Properties • Temperature = “degree of hotness” • Rapidly moving molecules (atoms) have a high temperature • Slowly moving molecules (atoms) have a low temperature

  6. F A Weight Impact Thermodynamic Properties • Pressure - force per unit area

  7. Low density High density Thermodynamic Properties • Density - mass per unit volume

  8. ………. … ………………... Thermodynamic Properties • Amount of Substance – how much is there 1 2 3 12 144 6.022 × 1023 Dozen Gross Avogadro’s Number

  9. Pair Exercise 1 • A cube of osmium measures 0.2 m on a side. It sits on a table. At the contact between the table and osmium, calculate the pressure (N/m2). Note: Densities may be found in Table 11.1 Foundations of Engineering

  10. Solid Liquid Gas Plasma States of Matter

  11. Pressure Liquid Pcritical Critical Point Plasma Solid Ptriple Triple Point Gas Vapor Ttriple Tcritical Temperature Pressure, Temperature, and State

  12. Gas Laws • apply only to perfect (ideal) gases • Boyle’s Law • Charles’ Law • Gay-Lussac’s Law • Mole Proportionality Law

  13. P2 V2 P1 V1 T = const n = const Boyle’s Law

  14. T2 V2 T1 V1 P = const n = const Charles’ Law

  15. T2 P2 T1 P1 V = const n = const Gay-Lussac’s Law

  16. n2 V2 n1 V1 T = const P = const Mole Proportionality Law

  17. Perfect Gas Law • The physical observations described by the gas laws are summarized by the perfect gas law (a.k.a. ideal gas law) PV = nRT P = absolute pressure V = volume n = number of moles R = universal gas constant T = absolute temperature

  18. Values for R

  19. Pair Exercise 2 • A balloon is filled with air to a pressure of 1.1 atm. The filled balloon has a diameter of 0.3 m. • A diver takes the balloon underwater to a depth where the pressure in the balloon is 2.3 atm. • If the temperature of the balloon does not change, what is the new diameter of the balloon?

  20. = Energy • Energy is the capacity to do work, but work is a form of energy... • It is easier to think of energy as a scientific and engineering “unit of exchange”, much like money is a unit of exchange. • Example • 1 car = $20k • 1 house = $100k • 5 cars = 1 house

  21. Energy Equivalents A case for nuclear power? • 1 kg coal = 42,000,000 joules • 1 kg uranium = 82,000,000,000,000 joules (82x1012) • 1 kg uranium = 2,000,000 kg coal!!

  22. Heat • Heat is the energy flow resulting from a temperature difference. • NOTE: HEAT AND TEMPERATURE ARE NOT THE SAME!

  23. T = 100oC Temperature Profile in Rod T = 0oC Heat Vibrating copper atom Copper rod Example

  24. Work • Heat flows due to a temperature “driving force” • Work is the energy flow from any other driving force

  25. Types of Work

  26. F F D x Mechanical Work

  27. i.e., work is the area under the F vs. x curve (assume F is not a function of x) Mechanical Work

  28. F DV Dx A F P P P = const PV Work (Hydraulic)

  29. Pair Exercise 3 An ideal gas is contained in a closed system. Under constant pressure, the container is compressed from V1 to V2 (volume). Derive the equation for work in terms of the universal gas constant and temperature.

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