Chapter 12 The Laws of Thermodynamics 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 Converting Internal Energy to Mechanical U Q P V Work done by expansion W F x F PA x V A W P V 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 1 950x105 Pa b If the gas expands such that the cylinder rises 12 0 cm what work was done by the gas 183 8 J c What amount of the work went into changing the gravitational PE of the piston 88 3 J d Where did the rest of the work go Compressing the outside air 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 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 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 a previous pressure Greater than b Less than c Equal to Some Vocabulary P Isobaric V P constant Isovolumetric P V V constant Isothermal T constant Adiabatic Q 0 P V P V Example 12 3a Outside Air Room T Atm P 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 Pb is Pa a Greater than b Less than c Equal to U Q P V W P V Example 12 3b Outside Air Room T Atm P 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 Tb is Ta a Greater than b Less than c Equal to U Q P V W P V Example 12 3c Outside Air Room T Atm P 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 Wab is 0 a Greater than b Less than c Equal to U Q P V W P V ocabulary Wab is work done by gas between a and b Example 12 3d Outside Air Room T Atm P 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 Ub is Ua a Greater than b Less than c Equal to U Q P V W P V Example 12 3e Outside Air Room T Atm P 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 Qab is 0 a Greater than b Less than c Equal to U Q P V W P V Vocabulary Qab is heat added to gas between a and b Example 12 4a Outside Air Room T Atm P 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 adiabatically compressing the gas to half its original volume b Pb is Pa a Greater than b Less than c Equal to U Q P V W P V Example 12 4b Outside Air Room T Atm P 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 adiabatically compressing the gas to half its original volume b Wab is 0 a Greater than b Less than c Equal to U Q P V W P V Example 12 4c Outside Air Room T Atm P 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 adiabatically compressing the gas to half its original volume b Qab is 0 a Greater than b Less than c Equal to U Q P V W P V Example 12 4d Outside Air Room T Atm P 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 adiabatically compressing the gas to half its original volume b Ub is Ua a Greater than b Less than c Equal to U Q P V W P V Example 12 4e Outside Air Room T Atm P 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 adiabatically compressing the gas to half its original volume b Tb is Ta a Greater than b Less than c Equal to U Q P V W P V Example 12 5a Outside Air Room T Atm P 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 The gas is cooled isobarically compressing the gas to half its original volume b Pb is Pa a Greater than b Less than c Equal to PV nRT U Q P V W P V Example 12 5b Outside Air Room T Atm P 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 The gas is cooled isobarically compressing the gas to half its original volume b Wab is 0 a Greater than b …
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