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THERMODYNAMICS

THERMODYNAMICS. Heat and Work. THERMODYNAMICS. Thermodynamics looks at how changes in energy, work and the flow of heat influence each other. LAWS OF THERMODYNAMICS. FIRST LAW OF THERMODYNAMICS.

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THERMODYNAMICS

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  1. THERMODYNAMICS Heat and Work

  2. THERMODYNAMICS • Thermodynamics looks at how changes in energy, work and the flow of heat influence each other.

  3. LAWS OF THERMODYNAMICS

  4. FIRST LAW OF THERMODYNAMICS • The heat gained or lost in a system Is equal to the increase or decrease in the internal energy of the system plus the work done on the system

  5. Total Heat = Change In Initial energy + Work Done Q = ∆U + W

  6. Q = ∆U + W • Q is positive if you add heat to the system and negative if you remove heat from the system. • W is positive if the work is done by the system, and negative if work Is done on the system. • ∆U is arbitrary and can be expressed in terms of Q and W

  7. A gas in a system has constant pressure. The surroundings around the system lose 62J of heat and does 474J of work onto the system. What is the internal energy of the system?

  8. The surrounding area loses heat and does work onto the system. Therefore “q” and “w” are positive in equation because the system gains heat and gets work done on and by itself. (62J) + (474J) = 536 J

  9. SECOND LAW OF THERMODYNAMICS • It is impossible for heat to flow from a point of lower temperature to a point of higher temperature without the application of energy from an external source.

  10. Cooling devices make us of coolants like Freon.

  11. The refrigerator is colder than the room where it is located. Why is it then that the flow of heat is from the refrigerator to the room? Cooling devices like air-conditioners have exhaust where hot air comes out.

  12. Low Temperature Higher Temperature HEAT FLOW THE ROOM

  13. COOLANT AROUND REFRIGERATOR THE ROOM Lower T HEAT FLOW WASTED HEAT High T THERMALEQUILIBRIUMCOLD STORAGE STORAGE AREA EXTERNAL ENERGY THE MOTOR ELECTRICAL ENERGY HEAT FLOW (EXHAUST) MECHANICAL ENERGY

  14. ENTROPY • Wasted Heat • Measure of the amount of disorder in the system Entropy Change = Heat added Temperature ( in Kelvin)

  15. The entropy changes for reversible processes are bigger than those for non-reversible processes which have friction. • Over time, the amount of entropy in the universe increases.

  16. COOL EXAMPLES What appliance can actually cool a room? • A Fan ( electric, not moving)? • A Refrigerator with the door open? • A Refrigerator with it’s door closed? • An Air conditioner on the middle of the room? • An Air Conditioner partially exposed outside?

  17. The Air Conditioner that is partially exposed ( back to outside) can lower the internal energy of the room. Removes heat and exhausts it outside the room Some consume electrical energy that increases the room’s total internal energy. Wasted Heat

  18. When water vapor condenses in the air, how does the heat flow? Release Heat Air becomes warmer

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