Phys10 - Unit 10 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8...

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1 Unit 10 Laws of Thermodynamics and Thermal Processes 10.1 Temperature scale 10.2 Thermodynamic temperature and absolute zero 10.3 Gas Laws 10.4 Kinetic theory 10.5 The internal energy of an ideal gas 10.6 Important terms used in thermodynamics 10.7 The zeroth law of thermodynamics 10.8 The first law of thermodynamics 10.9 Thermal Processes 10.10 Specific heats for an ideal gas 10.11 The second law of thermodynamics 10.12 The third law of thermodynamics 10.1 Temperature scale The Fahrenheit scale goes from 32 o to 212 o (a total of 180 divisions). The Celsius scale goes from 0 o to 100 o (a total of 100 divisions). Fahrenheit o F Celsius o C Boiling of water 212 100 Freezing of water 32 0 Now, we have 100 C o correspond to 180 F o , that is, 1C o corresponds to 180/100 F o , or 1C o corresponds to (9/5) F o . Here, we have a formula to relate C o and F o C F T T 5 9 32 + = . Example Two thermometers, one marked in Fahrenheit the other in Celsius, are placed in a bath. At what temperature will both thermometers read the same?
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2 Answer: The same reading will occur at T , where ) 32 ( 9 5 = T T gives T = 40 o . 10.2 Thermodynamic temperature and absolute zero Pressure versus temperature for a gas at constant volume As the gas is cooled, its atoms lose some of their thermal energy; they travel more slowly and collide with the chamber walls less frequently and less forcefully, As a result, the pressure in the chamber drops. A plot of pressure versus temperature is shown below. All gases show straight lines of the same intercept at 273.15 o C, but different gases have different slopes. Volume versus temperature for a gas at constant pressure As the temperature of a gas is lowered, its atoms are less energetic. To keep the pressure constant, the volume must decrease, which will make it easier for atoms to strike the chamber walls frequently, thereby sustaining the pressure. All gases shrink toward zero volume at T = 273.15 o C. T ( o C) 273.15 0 P T ( o C) 273.15 0 V
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3 The 273.15 o C is referred as the absolute zero temperature. An absolute temperature is given a SI unit, Kelvin K, in which 0 K corresponds to 273.15 o C; and has the same size as Celsius; therefore 0 o C corresponds to 273.15 K. In general, the temperature in Kelvin relates the Celsius degree by the relation T = T C + 273.15. 10.3 Gas Laws Boyle’s law Keeping the temperature constant, the volume of a gas varies inversely with the pressure, which is equivalent to saying that pressure times volume is constant. P V 1 or PV = constant Charles’s law When the pressure is kept constant, the volume of a given amount of any gas varies directly with the temperature (in Kelvin). T V or constant = T V Gay-Lussac’s law When the volume is kept constant, the absolute pressure of a given amount of any gas varies directly with the temperature (in Kelvin).
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Phys10 - Unit 10 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8...

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