Gas Laws & Absolute Gas Laws & Absolute ZeroZero

Thermal Physics Lesson 3Thermal Physics Lesson 3

Learning ObjectivesLearning Objectives

State the three gas laws, describing the State the three gas laws, describing the relationships between p,V,T and mass.relationships between p,V,T and mass.

Describe how the thermodynamic scale Describe how the thermodynamic scale is defined.is defined.

Define absolute zero.Define absolute zero.

Convert temperatures between Celsius Convert temperatures between Celsius and Kelvin.and Kelvin.

Thermodynamic Thermodynamic Temperature ScaleTemperature Scale

A change of 1 K equals a change of 1 A change of 1 K equals a change of 1 ooC.C.

To convert from degrees Celcius into To convert from degrees Celcius into kelvin add 273.15:-kelvin add 273.15:-

15.273CK

DefinitionDefinition

Absolute ZeroAbsolute Zero is the lowest possible is the lowest possible temperature, and something at this temperature, and something at this temperature has the lowest possible temperature has the lowest possible internal energy.internal energy.

This is zero kelvin, written 0 K, on the This is zero kelvin, written 0 K, on the thermodynamic temperature scale.thermodynamic temperature scale.

DefinitionDefinition

The internal energy of an object is the The internal energy of an object is the sum of the random distribution of the sum of the random distribution of the kinetic and potential energies of its kinetic and potential energies of its molecules.molecules.

Boyle’s LawBoyle’s Law

Temperature and moles of gas are Temperature and moles of gas are constant constant

Graph is hyperbolic (see below) and Graph is hyperbolic (see below) and asymptotic to both axes asymptotic to both axes

Pressure and volume are inversely Pressure and volume are inversely proportional to each other proportional to each other

Vp

1

Ideal Gas vs. Perfect GasIdeal Gas vs. Perfect Gas

Strictly speaking an ideal gas is one Strictly speaking an ideal gas is one that obeys Boyle’s law with complete that obeys Boyle’s law with complete precision. precision.

A perfect gas is a real gas under A perfect gas is a real gas under conditions that Boyle’s law is a valid conditions that Boyle’s law is a valid enough description of its behaviour.enough description of its behaviour.

Charles’ LawCharles’ LawPressure and moles of gas are Pressure and moles of gas are constant constant Graph is linear (see right) Graph is linear (see right) Volume and temperature are directly Volume and temperature are directly proportional to each other proportional to each other

TV

Pressure Law (Gay-Lussac's Pressure Law (Gay-Lussac's Law )Law )

Volume and moles of gas are Volume and moles of gas are constant constant Graph is linear (see right) Graph is linear (see right) Pressure and temperature are Pressure and temperature are directly proportional to each directly proportional to each other other

Tp