2 Thermal PhysicsTopicsTemperature and the zeroth Law of ThermodynamicsThermometers and Temperature ScalesThermal Expansion of Solids and LiquidsMicroscopic Description of an Ideal GasThe Kinetic Theory of Gases
3 A B C Temperature and the zeroth Law of Thermodynamics Two objects placed in thermal contact will eventually come to the same temperature. When they do, we say they are in thermal equilibrium.The Zeroth Law of ThermodynamicsABCIf A is in thermal equilibrium with Cand B is in thermal equilibrium with CThen A and B are in thermal equilibrium.
4 Thermometers and Temperature Scales Temperature is a measure of how hot or cold something is.Thermometers are instruments designed to measure temperature. In order to do this, they take advantage of some property of matter that changes with temperature.Most materials expand when heated.
5 Thermometers and Temperature Scales Common thermometers used today include the liquid-in-glass type and the bimetallic strip.
6 Thermal Physics 10-01A bimetallic strip, consisting of metal G on the top and metal H on the bottom, is rigidly attached to a wall at the left as shown. In the diagram. The coefficient of linear thermal expansion for metal G is greater than that ofmetal H. If the strip is uniformly heated, it will(A) curve upward.(B) curve downward.(C) remain horizontal, but get longer.(D) bend in the middle.
7 Thermometers and Temperature Scales Temperature is generally measured using either the Kelvin, Celsius, or the Fahrenheit scale.CelsiusFahrenheitKelvinBoilingPoint (H2O)373100212MeltingPoint (H2O)27332Absolute Zero-273-459
8 Thermal Expansion of Solids and Liquids Expansion occurs when an object is heated.A steel washeris heatedDoes the hole increaseor decrease in size?
9 Thermal Expansion of Solids and Liquids When the washeris heatedThe holebecomeslarger
10 Thermal Physics 10-02Consider a flat steel plate with a hole through its center as shown in the diagram. When the plate's temperature is increased, the hole will(A) expand only if it takes up more than halfthe plate's surface area.(B) contract if it takes up less than half(C) always contract.(D) always expand.
11 Thermal Expansion of Solids and Liquids LoDL LoDTDTDL = aLoDTL - Lo = aLoDTCoefficient oflinear expansionL = Lo(1+aDT)
12 Thermal Expansion of Solids and Liquids (Problem) sleeveshaftDdA cylindrical brass sleeve is to be shrunk-fitted over a brass shaft whose diameter is cm at 0 oC. The diameter of the sleeve is cm at 0 oC.To what temperature must the sleeve be heated before it will slip over the shaft?
13 Thermal Expansion of Solids and Liquids (Problem) shaftsleeveDdTo what temperature must the sleeve be heated before it will slip over the shaft?
14 Thermal Expansion of Solids and Liquids Volume ExpansionLo + DLLoNew VolumeInitial VolumeDL = aLoDT
15 Thermal Expansion of Solids and Liquids CoefficientofVolumeExpansion
16 Thermal Expansion of Solids and Liquids (Problem) An automobile fuel tank is filled to the brim with 45 L of gasoline at 10 oC. Immediately afterward, the vehicle is parked in the Sun, where the temperature is 35 oC. How much gasoline overflows from the tank as a result of expansion?Change involumeof the steelgas tankOverflowChange involumeof thegasoline
17 Microscopic Description of an Ideal Gas Volume(m3)Pressure(Pa)AbsoluteTemperature(K)PV = nRTGas Quantity(mol)Gas Constant(8.31 J/molK)(L.atm)/(mol.K)1.99 cal/(mol.K)
18 Thermal Physics 10-03Both the pressure and volume of a given sample of an ideal gas double. This means that its temperature in Kelvin must(A) double.(B) quadruple.(C) reduce to one-fourth its original value.(D) remain unchanged.~M1~M2~M3~M4~M5~M6~M7~M8~M10~M9~M11~M12~M13~M14~M15~M16~M17~M18~M20~M19~M21~M22~M23~M24~M25~M26~M27~M28~M30~M29~M31~M32~M33~M34~M35~M36~M37~M38~M40~M39~M41~M42~M43~M44~M45~M46~M47~M48~M50~M49~M51~M52~M53~M54~M55~M56~M57~M58~M60~M59
19 Microscopic Description of an Ideal Gas A mole (mol) is defined as the number of grams of a substance that is numerically equal to the molecular mass of the substance:1 mol H2 has a mass of 2 g1 mol Ne has a mass of 20 g1 mol CO2 has a mass of 44 gThe number of moles in a certain mass of material:The number of moles in a certain number of particles:
20 Microscopic Description of an Ideal Gas Volume(m3)Pressure(Pa)PV = NkTAbsoluteTemperature(K)Number ofMoleculesBoltzmann’sConstant(1.38 x J/K)
21 Microscopic Description of an Ideal Gas Boltzmann’s ConstantGasConstantAvogadro’sNumber
22 Microscopic Description of an Ideal Gas (Problem) A gas is contained in an 8.0 x 10-3 m3 vessel at 20 oCand a pressure of 9.0 x 105 N/m2.(a) Determine the number of moles of gas in the vessel.
23 Microscopic Description of an Ideal Gas (Problem (con’t)) A gas is contained in an 8.0 x 10-3 m3 vessel at 20 oCand a pressure of 9.0 x 105 N/m2.(b) How many molecules are in the vessel?
24 Thermal Physics 10-04A container of an ideal gas at 1 atm is compressed to one-third its volume, with the temperature held constant. What is its final pressure?(A) 1/3 atm(B) 1 atm(C) 3 atm(D) 9 atm
25 Microscopic Description of an Ideal Gas 0.20 x 105 Pa0.80 x 105 PaA cylinder with a moveable piston contains gas at a temperature of 27 oC, a volume of 1.5 m3, and an absolute pressure of 0.20 x 105 Pa.1.5 m327 oC0.70 m3
26 Microscopic Description of an Ideal Gas (Problem) 0.20 x 105 Pa0.80 x 105 PaWhat will be its final temperature if the gas is compressed to 0.70 m3 and the absolute pressure increases to 0.80 x 105 Pa?1.5 m327 oC0.70 m3
27 The Kinetic Theory of Gases Assumptions of kinetic theory:1) large number of molecules, moving inrandom directions with a variety of speeds2) molecules are far apart, on average3) molecules obey laws of classical mechanics andinteract only when colliding4) collisions are perfectly elastic
28 The Kinetic Theory of Gases xyzvLAThe force exerted on the wall by the collision of one molecule of mass m isThen the average force due to N molecules colliding with that wall is
29 The Kinetic Theory of Gases xyzvLAThe averages of the squares of the speeds in all three directions are equal:So the pressure on the wall is:
30 The Kinetic Theory of Gases Rewriting,soThe average translational kinetic energy of the molecules in an ideal gas is directly proportional to the temperature of the gas.
31 The Kinetic Theory of Gases Molecular Kinetic EnergyTemperature is a measure of the averagemolecular kinetic energy.
32 Thermal Physics 10-05According to the ideal gas Law, PV = constant for a given temperature. As a result, an increase in volume corresponds to a decrease in pressure. This happens because the molecules(A) collide with each other more frequently.(B) move slower on the average.(C) strike the container wall less often.(D) transfer less energy to the walls of the containereach time they strike it.
33 Thermal Physics 10-06The absolute temperature of an ideal gas is directly proportional to which of the following?(A) speed(B) momentum(C) kinetic energy(D) mass
34 Thermal Physics 10-07Oxygen molecules are 16 times more massive than hydrogen molecules. At a given temperature, the average molecular kinetic energy of oxygen, compared to hydrogen(A) is greater.(B) is less.(C) is the same.(D) cannot be determined since pressure andvolume are not given
35 The Kinetic Theory of Gases (Problem) What is the total random kinetic energy of all themolecules in one mole of hydrogen at a temperatureof 300 K.Kinetic energyper moleculeAvogadro’snumber
36 The Kinetic Theory of Gases (Problem) Calculate the rms speed of a Nitrogen molecule (N2)when the temperature is 100 oC.Mass of N2 molecule:rms speed:
37 The Kinetic Theory of Gases (Problem) If 2.0 mol of an ideal gas are confined to a 5.0 L vessel ata pressure of 8.0 x 105 Pa, what is the average kineticenergy of a gas molecule?Temperature of the gas:Kinetic energy:
38 Thermal Physics 10-08A container holds N molecules of an ideal gas at a given temperature. If the number of molecules in the container is increased to 2N with no change in temperature or volume, the pressure in the container(A) doubles.(B) remains constant.(C) is cut in half.(D) none of the above
39 The Kinetic Theory of Gases 523614Mean and rms SpeedMean Speed:rms Speed:
40 Thermal Physics 10-09A sample of an ideal gas is slowly compressed to one-half its original volume with no change in temperature. What happens to the average speed of the molecules in the sample?(A) It does not change.(B) It doubles.(C) It halves.(D) none of the above
41 Thermal Physics 10-10A mole of diatomic oxygen molecules and a mole of diatomic nitrogen molecules at STP have(A) the same average molecular speeds.(B) the same number of molecules.(C) the same diffusion rates.(D) all of the above
42 SummaryTemperature is a measure of how hot or cold something is, and is measured by thermometers.There are three temperature scales in use: Celsius, Fahrenheit, and Kelvin.When heated, a solid will get longer by a fraction given by the coefficient of linear expansion.The fractional change in volume of gases, liquids, and solids is given by the coefficient of volume expansion.
43 SummaryIdeal gas law:One mole of a substance is the number of grams equal to the atomic or molecular mass.Each mole contains Avogadro’s number of atoms or molecules.The average kinetic energy of molecules in a gas is proportional to the temperature: