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Physis 202, CH. 12 Book Notes

by: Melissa

Physis 202, CH. 12 Book Notes PHYS 202

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These notes cover all off Ch. 12 notes
General Physics >4
Jenkins T
Class Notes
Physics, Thermal properties of matter
25 ?




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This 6 page Class Notes was uploaded by Melissa on Thursday January 7, 2016. The Class Notes belongs to PHYS 202 at University of Oregon taught by Jenkins T in Fall 2015. Since its upload, it has received 18 views. For similar materials see General Physics >4 in Physics 2 at University of Oregon.


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Date Created: 01/07/16
Molecules bumping into each other creates pressure Molecules at a faster speed increase the temperature An increase in temperature increases the pressure which causes expansion because they are hitting the walls more frequently and with more force • 12.1 The atomic model of matter ⿞Phases ‣ Gas: system in which each particle moves freely through space until it collides with another particle or wall of its container ‣ Liquid: weak bonds permit motion while keeping the particles close together ‣ Solid: definite shape and can be compressed or deformed only slightly ⿞Atomic Mass and Atomic Mass Number ‣ Atomic mass number: sum of the protons and neutrons in the nucleus ‣ Molecular Mass: sum of the atomic masses of the atoms that form the molecule ⿞Definition of the Mole ‣ • Called Avogadro's number ‣ Molar mass: ‣ • Ex. 100g of oxygen and has molar mass of 32g/mol. How many moles are there? ⿞ ⿞Volume ‣ Characteristic of a macroscopic system • 12.2 The atomic model of an ideal gas ⿞Gases are compressible because their particles are so spread out whereas in liquids and solids, the particles are either fairly close to each other or are in direct contact ⿞Temperature of an ideal gas is directly proportional to the average kinetic energy per atom ‣ ‣ ‣ ‣ ‣ Thermal energy is proportional to change in temperature ⿞Molecular Speeds and Temperature ‣ RMS speed: • The speed of an atom with the average kinetic energy • Also related to the speed ⿞ • RMS speed is proportional to the square root of the temperature • Remember that changing x by a factor of c changes y by a factor of. ‣ Pressure • Collisions exert a force on wall they hit and net force causes gas to have a pressure • Area is proportional to the force exerted ⿞twice as big a circle means twice as many particles and thus double the force ⿞Pressure in a gas ‣ ⿞Be aware that pressure is not a force but a force creates the pressure ⿞Measured in pascals ‣ ‣ • A net pressure force is exerted only where there is a pressure difference between the two sides of a surface ⿞Ex. Force that holds the lid on a vacuum sealed jar where the pressure inside is less than the pressure outside ‣ To remove the lid, you have to exert a force greater than the force due to the pressure difference • Decreasing number of moles decreases the pressure ⿞From Collisions to Pressure and the Ideal Gas Law ‣ • Gas Law Video ⿞If you have a container with a constant volume and you make it extremely cold, what happens to the pressure? ‣ Pressure decreasing because the molecules are not moving as fast ⿞At a constant pressure, as the temperature increases the volume will also increase ⿞As you keep the temperature constant at room temperature but are decreasing the pressure, your volume will increase ‣ Inverse relationship • 12.3 Ideal Gas Processes ⿞Gas is a fixed quantity ‣ In sealed containers the number of moles does not change so: • Final and initial states related by: ⿞PV diagrams ‣ Points represent the state of the gas ⿞Constant volume processes ‣ Gas in closes container: warming gas increases pressure but keeps volume the same so • On a graph it would be represented as a vertical line • ⿞Constant Pressure ‣ Called isobaric ‣ Found when there is a piston that is free to slide up and down which allows for the compression or expansion of gas until reaching • The equilibrium position where • If gas is heated in a cylinder, the pressure does not change because pressure is controlled by unchanging external pressure ⿞Will cause the piston to move up because molecules are moving so fast ⿞Represented as a horizontal line ⿞Constant Temperature ‣ Isothermal ‣ Occurs like in a situation where a container of gas is submerged in container of liquid that is at a constant temp • Causes piston to be pushed slowly which transfers heat and energy through the walls ⿞Isothermal compression ‣ Reverse is isothermal expansion ‣ There is an inverse relationship between P and V so graph is a hyperbola ⿞Thermodynamics of ideal gas processes ‣ When gases expand they are doing work by pushing a piston ‣ Work done in a isobaric process • • For gas to do work, volume must change • Equation only works with constant pressure processes • Work is positive if gas expands • Work is negative if gas is compressed or if energy is transferred out of the system • First law of thermodynamics can be written as • Thermal energy of ideal gas can be written as ⿞ ‣ Adiabatic Processes • Remember Doing work on a gas increases the thermal energy • When Q= 0 for expansion or compression then it is adiabatic ⿞Temperature will decrease in adiabatic expansion ⿞Temp increases in adiabatic compression • Allows you to use work rather than heat to change temperature of a gas • 12.4 Thermal Expansion ⿞ ‣ Equation for volume thermal expansion ‣ Beta is the coefficient of volume expansion • Value depends on the material the object is made of ⿞Equation for linear thermal expansion : ‣ Alpha is the coefficient of linear expansion ⿞Special Properties of Water and Ice ‣ As water approaches the freezing point, molecules begin to form clusters that are more strongly bound and thus get farther apart to form clusters so volume increases ‣ Water expands significantly when making the transition from liquid to solid ‣ When becoming solid it becomes more dense • 12.5 Specific Heat and Heat of Transformation ⿞Amount of heat that raises the temp of 1kg of a substance by 1 K ⿞Heat needed to produce a temperature change with specific heat c: ‣ ‣ Q can be positive(temp goes up) or negative( temp goes down) ‣ Takes a large amount of heat energy to change the temperature of a substance with a large specific heat ⿞Phase changes ‣ Temperature is constant and does not increase when it is changing phases ‣ Only increases when something is being warmed or cooled ‣ Thermal Energy of a solid is the kinetic energy of the vibrating atoms plus the PE of stretched and compressed molecular bonds • When being heated, thermal energy gets large and this bonds break and move around: solid is melting ‣ When thermal energy is reduced or when a solid becomes liquid: melting pt • At the melting point, system is in phase equilibrium ‣ Temperature where liquid becomes a gas is the boiling point ‣ Gas to liquid: condensation ⿞Heat transformation ‣ During the phase changes, thermal energy continues to be added but only to break bonds, not to increase the temperature ‣ Heat transformation use the symbol : L • The amount of energy that causes a kg of a substance to undergo. Phase change • Heat of fusion( solid and liquid) and heat of vaporization ( liquid and gas) ⿞ ⿞Evaporation ‣ Water evaporates as sweat below the boiling point of water (100*C) ‣ In gases: different molecules have different speeds and some will go into The gas phase and thus they take thermal energy with them • They have the highest KE so evaporation reduces the average KE and the temperature of liquid left behind • Sweating is also a sign of body exhausting excess heat • 12.6 Calorimetry ⿞The quantitative measurement of the heat transferred between systems or evolved in reactions ⿞Insulation prevents an heat energy from being transferred to or from the environment ‣ If energy enters the system, Q is positive ‣ Negative if it leaves the system ‣ • 12.7 Specific Heat of Gases ⿞Quantity of heat needed to change the temperature of n moles of gas by the change in temperature for constant volume processes: ‣ For constant pressure: ‣ Is the molar specific heat at constant volume while The molar specific heat for constant pressure ‣ If you heat a gas in a sealed container so that there is no change in volume, then no work is done ‣ If you heat gas with a piston to keep it at constant pressure, then the gas will cause it to expand and work is done ‣ Molar specific heats ar Higher for monatomic gases because they only have the translational KE and thus allows it to move faster when heated • While diatomic has rotational KE as well ‣ Regualar specific heat is greater for diatomic molecules • 12.8 Heat Transfer ⿞Conduction ‣ Transfer of thermal energy directly theough a physical material ‣ The faster moving molecules on the hotter end transfer energy to the slower molecules ‣ Q increases if temperature difference between hot and cold is increased ‣ Q increases if cross section is increased ‣ Q decreases if length of the rod is increases ‣ Rate of conduction • ⿞K is the thermal conductivity of the material ⿞Convection ‣ When the heat expands and becomes less dense than wate above it, it rises to the surface while cooler denser water sinks ‣ Transfer of thermal energy by the motion of a fluid ⿞Radiation ‣ Where heat energy is transferred to your body ‣ Consists of electromagnetic waves ‣ Transfer energy from object that emits radiation to object that absorbs it ‣ Body absorbs heat from outside and radiates heat outward to get rid of it ‣ Rate of transfer by radiation ‣ • E is the emissivity or a ,easier of the effectiveness of radiation; between 0 and 1 •


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