ch13 - Temperature and Kinetic Theory Chapter Outline...

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Unformatted text preview: Temperature and Kinetic Theory Chapter Outline GENERAL PHYSICS Temperature and Thermometers PHY 302K Thermal Equilibrium and the Zeroth Law of Thermodynamics Thermal Expansion Chapter 13: Temperature and Kinetic Theory Macroscopic Description of an Ideal Gas Maxim Tsoi The Kinetic Theory of Gases Physics Department, The University of Texas at Austin 302K - Ch.13 302K - Ch.13 Temperature Thermal Physics Study of temperature, heat, and how they affect matter • How a trapped water blow off the top of volcano in a giant explosion? • What causes roads to fracture and buckle when temperature changes? • How can thermal energy do work, e.g., running engines? Zeroth law of thermodynamics • Temperature commonly associated with how hot or cold an object feels when we touch it (unreliable) • Thermometer reliable method to measure the relative “hotness” or “coldness” of objects related only to temperature • Thermal contact energy can be exchanged between objects • Thermal equilibrium no net exchange of energy between objects • Ideal Gas collection of non-interacting point particles in thermal equilibrium • Ideal Gas Law relates macroscopic properties: pressure, volume, temperature, and number of particles associated with gas • Kinetic Theory of Gases how processes on the atomic scale affect macroscopic properties like pressure, temperature • If objects A and B are separately in thermal equilibrium with a third object C, then A and B are in thermal equilibrium with each other The objects in thermal equilibrium with each other are at the same temperature 302K - Ch.13 302K - Ch.13 Thermometers Thermal Expansion of Solids and Liquids Coefficient of linear expansion Temperature scales • Thermometers devices used to measure • T of substance increases substance’s volume increases ! temperature L L0 T • Make use of temperature-dependent • for small changes in T physical property volume of liquid/solid, gas pressure/volume, electric resistance, color • Celsius scale freezing/boiling points at 0oC/100oC TC TK 273.15 TF TC 32 9 5 • Kelvin scale absolute zero (-273.15oC) is 0 K and 1K=1oC Applications thermal expansion joints in buildings, concrete • Fahrenheit common in the US highways, and bridges; bimetallic strips and thermostats; 302K - Ch.13 302K - Ch.13 1 Ideal Gas The Kinetic Theory of Gases Macroscopic description Assumptions of microscopic description • Ideal Gas collection of atoms or molecules (point-like particles) that move randomly and exert no long-range forces on each other • Macroscopic processes can be understood on the basis of what is happening on the atomic scale ! • Equation of State relates pressure P, volume V, temperature T, and amount n of gas (number of moles) n m ; molar mass • Assumptions of microscopic theory: N A 6.02 1023 • N (number of molecules) is large; av. separation >> dimension • Molecules obey Newton’s laws of motion; move randomly molar mass in grams = atomic mass in u PT const ~ 1 / V • Interact only during elastic collisions • Charlles’s law VP const ~ T • Elastic collisions with walls • Gay-Lussac’s law PV const ~ T • Boyle’s law • All molecules are identical PV nRT PV NkBT • Ideal Gas Law or R=8.31 J/mol*K kB=R/NA=1.38*10-23 J/K 302K - Ch.13 302K - Ch.13 The Kinetic Theory of Gases The Kinetic Theory of Gases Molecular model for pressure Molecular interpretation of temperature • Temperature direct measure of the • P result of molecules’ collisions with container’ walls F1 • Force exerted by one molecule: • by all molecules: average molecular kinetic energy of the gas 2 px 2mv x mv x d t t mv 2 3 k BT 2 2 2 m 2 Nm 2 Nm v 2 F v1 x v 2 x ... vx d d 3d P mv 2 PV 2 N 3 2 • Internal energy of monatomic gas • Root-mean-square (rms) speed 2 2 mv 3k B 2 T U 3 nRT 2 v rms v 2 3k BT m 2 F 2 N mv 3 2 A V 302K - Ch.13 302K - Ch.13 SUMMARY Temperature and Kinetic Theory • Zeroth law of thermodynamics If objects A and B are separately in thermal equilibrium with a third object C, then A and B are in thermal equilibrium with each other • Celsius/Kelvin TC TK 273.15 • Kelvin/Fahrenheit TF 9 TC 32 5 • Thermal Expansion • Ideal gas law L L0 T PV nRT • Kinetic theory of gases: P 2 3 2 N mv V 2 T 2 2 mv 3k B 2 • Internal energy of monatomic gas • Root-mean-square (rms) speed v rms 3k BT v m U 3 nRT 2 2 302K - Ch.13 2 ...
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