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# chapter12.key - The Laws of Thermodynamics Chapter 12 1...

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Unformatted text preview: The Laws of Thermodynamics Chapter 12 1 Principles of Thermodynamics • Energy is conserved • FIRST LAW OF THERMODYNAMICS • Examples: Engines (Internal -> Mechanical) Friction (Mechanical -> Internal) • All processes must increase entropy • SECOND LAW OF THERMODYNAMICS • Entropy is measure of disorder • Engines can not be 100% efficient 2 ! U = Q " P ! V Converting Internal Energy to Mechanical Work done by expansion W = F ! x , F = PA , ! x = ! V / A W = P ! V 3 Example 12.1 A cylinder of radius 5 cm is kept at pressure with a piston of mass 75 kg. a) What is the pressure inside the cylinder? b) If the gas expands such that the cylinder rises 12.0 cm, what work was done by the gas? c) What amount of the work went into changing the gravitational PE of the piston? d) Where did the rest of the work go? 1.950x10 5 Pa 183.8 J 88.3 J Compressing the outside air 4 Example 12.2a A massive copper piston traps an ideal gas as shown to the right. The piston is allowed to freely slide up and down and equilibrate with the outside air. The pressure inside the cylinder is _________ the pressure outside. a) Greater than b) Less than c) Equal to 5 Example 12.2b A massive copper piston traps an ideal gas as shown to the right. The piston is allowed to freely slide up and down and equilibrate with the outside air. The temperature inside the cylinder is __________ the temperature outside. a) Greater than b) Less than c) Equal to 6 Example 12.2c A massive copper piston traps an ideal gas as shown to the right. The piston is allowed to freely slide up and down and equilibrate with the outside air. If the gas is heated by a steady flame, and the piston rises to a new equilibrium position, the new pressure will be _________ than the previous pressure. a) Greater than b) Less than c) Equal to 7 Some Vocabulary • Isobaric • P = constant • Isovolumetric • V = constant • Isothermal • T = constant • Adiabatic • Q = 0 V V V V P P P P 8 A massive piston traps an amount of Helium gas as shown. The piston freely slides up and down. The system initially equilibrates at room temperature (a) Weight is slowly added to the piston, isothermally compressing the gas to half its original volume (b) P b is _______ P a Outside Air: Room T, Atm. P Example 12.3a a) Greater than b) Less than c) Equal to ! U = Q " P ! V W = P ! V 9 A massive piston traps an amount of Helium gas as shown. The piston freely slides up and down. The system initially equilibrates at room temperature (a) Weight is slowly added to the piston, isothermally compressing the gas to half its original volume (b) T b is ________ T a Outside Air: Room T, Atm. P Example 12.3b a) Greater than b) Less than c) Equal to ! U = Q " P ! V W = P ! V 10 A massive piston traps an amount of Helium gas as shown. The piston freely slides up and down....
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chapter12.key - The Laws of Thermodynamics Chapter 12 1...

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