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KIMIA LINGKUNGAN

KIMIA LINGKUNGAN. BAGIAN 2: TERMODINAMIKA. PREVIEW. In this third part of the course we: define and apply a number of thermodynamic ideas and concepts become familiar with and apply the 1st and 2nd law of thermodynamics

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KIMIA LINGKUNGAN

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  1. KIMIA LINGKUNGAN BAGIAN 2: TERMODINAMIKA

  2. PREVIEW In this third part of the course we: • define and apply a number of thermodynamic ideas and concepts • become familiar with and apply the 1st and 2nd law of thermodynamics • discuss several thermodynamic processes with the aid of pressure-volume (pV) diagrams • define and discuss the concept of entropy • apply the laws of thermodynamics to discuss heat engines, refrigerators and heat pumps • introduce parameters to quantify the efficiency at which thermodynamic devices operate • learn about the Carnot cycle and its relation to the concept of an 'ideal' engine

  3. Thermodynamic Systems, States and Processes Objectives are to: • define thermodynamics systems and states of systems • explain how processes affect such systems • apply the above thermodynamic terms and ideas to the laws of thermodynamics

  4. Thermodynamic Systems • A thermodynamic system is a collection of matter which has distinct boundaries.ORA real or imaginary portion of universe whish has distinct boundaries is called system.ORA thermodynamic system is that part of universe which is under thermodynamic study.

  5. 1. 1st Law of Thermodynamics • statement of energy conservation for a thermodynamic system • internal energy U is a state variable • W, Q process dependent

  6. Isoprocesses • apply 1st law of thermodynamics to closed system of an ideal gas • isoprocess is one in which one of the thermodynamic (state) variables are kept constant • use pV diagram to visualise process

  7. Isobaric Process • process in which pressure is kept constant

  8. Isochoric Process • process in which volume is kept constant

  9. Isothermal Process • process in which temperature is held constant

  10. Adiabatic Process • process in which no heat transfer takes place

  11. 2. Second Law of Thermodynamics and Entropy Objectives are to: • state and explain the second law of thermodynamics • explain the concept of entropy

  12. 2nd Law of Thermodynamics • states in which direction a process can take place • heat does not flow spontaneously from a cold to a hot body • heat cannot be transformed completely into mechanical work • it is impossible to construct an operational perpetual motion machine • introduces concept of entropy

  13. Entropy • property that indicates the direction of a process • entropy is a measure of disorder • entropy is a measure of a system’s ability to do useful work • entropy determines direction of time • the entropy of an isolated system increases

  14. 2nd Law of Thermodynamics: entropy

  15. 2nd Law example

  16. 3. Heat Engines and Heat Pumps Objectives are to: • explain what a heat engine is, and compute its thermal efficiency • explain what a heat pump is, and compute its coefficient of performance

  17. Diagram of a Heat Engine

  18. Heat Engine

  19. Heat Engine • A heat engine is a cyclic device that converts thermal energy into work output • It is a device that takes heat from a high-T reservoir, converts some of to (useful) work, and transfers the rest to the surroundings (a low-T reservoir) • Examples: steam engines; internal combustion engines (car engines) • Thermal efficiency (“what you get out/what you put in”): • No heat engine operating in a cycle can convert all of its heat input completely to work

  20. Heat Pump

  21. Heat Pump • A heat pump is a (cyclic) device that transfers heat energy from a low-T reservoir to a high-T reservoir • Examples: air conditioner; refrigerator • Coefficient of performance (“what you get out/what you put in”): • No heat pump operating in a cycle can transfer thermal energy to a low-T reservoir without doing some work

  22. Refrigerator (1)

  23. Refrigerator (2)

  24. 4. The Second Law Revisited • it is impossible to produce a cyclic engine that generates work by extracting heat from a reservoir without expelling some waste heat • it is impossible to produce a heat pump in which the sole result is the transfer of heat from a low-T to a high-T body

  25. 5. Third Law of Thermodynamics • The 3rd law states that: • It is impossible to reach a temperature of absolute zero • It is impossible to have a (Carnot) efficiency equal to 100% (this would imply Tc= 0).

  26. Isobaric Expansion: Change in Internal Energy • A quantity of an ideal gas has a volume of 22.4 litres at STP (standard temperature and pressure). While absorbing 315 cal of heat from the surroundings, the gas expands isobarically to 32.4 litres. What is the change in internal energy of the gas? • What is the equilibrium temperature (in degrees Celsius) of the gas after expansion?

  27. Question Three different experiments are run, in which a gas expands from point A to point D along the three paths shown below. Calculate the amount of work done for paths 1, 2 and 3.

  28. Questions • Free Loader: Consider the following idea. A ship heats its boilers and propels itself without the use of coal or oil in the following way. It pumps in warm sea water, extracts heat from that sea water, concentrates the extracted heat in its boilers, and discharges the cooled seawater back into the ocean. The discharged water may be ice if enough heat has been taken from it. Could this idea be made to work? • Gulf of Mexico: Another free loader idea is to generate power as follows. Water on top of the Gulf of Mexico is quite warm but deep down the water is cold. The plan is to heat some gas with warm water from the top so it will expand, and then cool the gas with water from the bottom so it will contract. The gas is alternately expanded and contracted so it drives a piston back and forth. The moving piston is attached by conventional means to an electric generator to make electricity. Can this idea be made to work?

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