Chapter 17
Phases and Phase Changes
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Phases and Phase Changes - General Physics - Lecture Slides, Slides of Physics
In these Lecture Slides, the Lecturer has put emphasis on the following key points : Phases and Phase Changes, Ideal Gases, Kinetic Theory, Solids and Elastic Deformation, Phase Equilibrium, Evaporation, Latent Heats, Phase Changes, Conservation, Easiest State
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2012/2013
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Chapter 17
Phases and Phase Changes
Units of Chapter 17
Ideal Gases
Kinetic Theory
Solids and Elastic Deformation
Phase Equilibrium and Evaporation
Latent Heats
Phase Changes and Energy
Conservation
If the volume of an idealgas is held constant, wefind that the pressureincreases withtemperature:
17-1 Ideal Gases
If the volume andtemperature are keptconstant, but more gas isadded (such as ininflating a tire orbasketball), the pressurewill increase:
17-1 Ideal Gases
17-1 Ideal Gases
Combining all three observations, we write
where
k
is called the Boltzmann constant:
17-1 Ideal Gases
Rearranging gives us the equation of state foran ideal gas:
Instead of counting molecules, we can countmoles. A mole is the amount of a substancethat contains as many elementary entities asthere are atoms in 12 g of carbon-12.
17-1 Ideal Gases
Avogadro’s number and the Boltzmann constantcan be combined to form the universal gasconstant and an alternative equation of state:
17-1 Ideal Gases
The atomic or molecular mass of a substanceis the mass, in grams, of one mole of thatsubstance. For example,Helium:Copper:Furthermore, the mass of an individual atomis given by the atomic mass divided byAvogadro’s number:
17-1 Ideal Gases
Charles’s law, alsoconsistent with theideal gas law, saysthat the volume of agas increases withtemperature if thepressure is constant.
17-1 Ideal Gases
In this photograph,the balloon wasinflated at roomtemperature andcooled with liquidnitrogen. Thedecrease in volumeof the air in theballoon is obvious.
17-2 Kinetic Theory
Pressure is the resultof collisions betweenthe gas moleculesand the walls of thecontainer. It depends on the mass and speed of themolecules, and on the container size:
17-2 Kinetic Theory
Not all molecules in a gas will have the samespeed; their speeds are represented by theMaxwell distribution, and depend on thetemperature and mass of the molecules.
17-2 Kinetic Theory
Comparing this expression with the ideal gaslaw allows us to relate average kinetic energyand temperature:^ The square root of
is called the root
mean square (rms) speed.
17-2 Kinetic Theory
Solving for the rms speed gives: