Thermal PhysicsChapter 10

Thermal PhysicsThermal physics looks at temperature, heat, and internal energyHeat and temperature are not the same thing although we use them interchangeably in our everyday language

ThermometerA device calibrated to measure the temperature (not heat) of an object

Zeroth Law of ThermodynamicsAKA the Law of EquilibriumIf 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.

TemperatureDefn: the property that determines whether or not an object is in thermal equilibrium with other objects

TemperatureTemperature is a measure of the intensity of heat or how hot a system is regardless of size. Kelvin is the official metric unitTo convert degrees Celsius to Kelvin by adding 273. To convert Kelvin to degrees Celsius subtract 273.

Thermal ExpansionDefn: as temperature increases, volume increasesEx. Useful in building designs, concrete highways, and bridges

Expressing Thermal ExpansionIf the thermal expansion of an object is sufficiently small compared with the objects initial dimensions, then the change in any dimension is proportional to the first power of the temperature change.

Defining the VariablesL0 initial length along some direction at some temperatureDL increase in lengthDT change in temperaturea = coefficient of linear expansion for a given material and has untis of 0C-1DL = aL0DT

Area Expansiong= coefficient of area expansionA = areaDA = A-A0 = gA0DT

Coefficient of Volume Expansionb= coefficient of volume expansionDV = bV0DT

ApplicationWhy would a glass break if it hot liquid is poured into it too quickly? You have a metallic lid stuck on a glass jar. Describe how you would loosen it without any tools.

Kinetic Molecular Theory of GasesA gas consists of small particles (atoms/molecules) that move randomly with rapid velocitiesThe attractive forces between particles of a gas can be neglectedThe actual volume occupied by a gas molecule is extremely small compared to the volume that gas occupies.The average kinetic energy of a gas molecule is proportional to Kelvin temperatureGas particles are in constant motion, moving rapidly in straight paths.

Properties of a gasPressure: kPa, atm, mm of Hg, torrConversion 760 mm Hg = 760 torr = 1 atm= 101.3 kPaVolume: L, mL or cm3Conversions 1000 mL = 1L 1 mL = 1 cmTemperature: 0C or KConversions 0C + 273 = K or 0C = K -273

Boyles Law:Pressure and volume are inversely proportional As pressure increases volume decreasesAs pressure decreases volume increasesPressure and Volume units must be the same on both sidesP1V1 = P2V2

Charles Law:Temperature and Volume are directly proportional As temperature increases volume increasesAs temperature decreases volume decreases Temperature must be in Kelvin (add 273)Volume units must be consistent on both sidesV1 / T1 = V2/T2

Gay-Lussacs Law:Pressure and Temperature are directly proportional As pressure increases temperature increasesAs pressure decreases temperature decreases Pressure units must be consistent on both sidesTemperature units must be in Kelvin (add 273)P1/T1 = P2/T2

Combined Gas Law: P1V1 = P2V2 T1 T2Pressure and volume and temperature vary according to this equation when all three changeTemperature must be in Kelvin

The Mole and Avagadros LawAvagadros Law: V1 / n1 = V2/n2n = number of moles, moles are large quantities of very small objects like molecules of a gasSTP = Standard Temperature and Pressure 00C or 273 K and 1 atm Molar volume: 22.4 L

Ideal Gas Law: (Eqn. of State)PV = nRT R is the universal gas constant and varies depending on which unit is used for measuring pressure R = 0.0821 L x atm. /mol or if using kPa R = 8.31 J/mol x K

Ideal Gas Law Using Boltzmanns ConstantPV= NkBTN = total number of moleculeskB = 1.38 x 10-23 J/K

Molecular Model of an Ideal GasThe pressure is proportional to the number of molecules per unit volume and the average translational kinetic energy of a molecule Temperature of a a gas is a direct measure of average molecular kinetic energy

Internal Energy, U, for a monatomic gasU = 3/2(nRT)Again, temperature must be in Kelvin

Root-mean-square (rms) speedVrms = square root of (3kBT/m) or = square root of (3RT/M)M is molar mass in kg/molThese speeds can be found on Table 10.2 on p. 324