Solids, Liquids and Gases

The Newtonian World
Thermal Physics
Solids, Liquids and Gases
Can you describe Solids, Liquids and
Gases in terms of
• Spacing
• Ordering
• and.........motion of molecules?
Kinetic Model for Solids
• Solids: particles have fixed positions close
together. Particles can vibrate about these
positions but do not have enough energy to
overcome the bonds holding them together.
Solids have a fixed, definite shape and volume.
They are incompressible, so they transmit
Kinetic Model for Liquids
• Liquids: particles are slightly further apart
than in solids- they have gained enough
energy to partially overcome the bonds
holding them together. Particles can move
freely, so that even though a liquid has a fixed
volume, it can take the shape of its container.
Liquids can be compressed very slightly, but
generally they are regarded as incompressible.
Liquids are fluids- they can flow and transmit
Kinetic Model for Gases
• Gases: particles are widely separated and
have high energy, leading to weak
intermolecular bonds (we often assume there
are no intermolecular bonds). Particles can
move freely and randomly, so gases take the
shape and volume of their container. About
99.99% of a gas’s volume is empty space.
Gases are also fluids, they can flow and
transmit pressure, even though in everyday
terms we only think of liquids as fluids.
Robert Brown – Brownian Motion
Brownian Motion
Describe an experiment that demonstrates Brownian
motion and discuss evidence for the movement of
molecules provided by such an experiment.
Useful information on Brownian
• Handy simulation 
• Wiki information (lots here, some way more than A-level
but good enrichment).
• Revision site 1 :
• Revision site 1 :
Pressure of Gases
• What is the definition of the term pressure?
• How can the kinetic theory be used to explain
the pressure exerted by gases? Explanation
based on Newton’s Laws!
What is the definition of internal
• What happens to the internal energy of body
when there is a temperature increase?
• What happens to the internal energy of body
when there is a change of state? What
happens to the temperature of a body when
there is a change of state?
Can you explain melting in terms of
the kinetic model?
Can you explain boiling in terms of
the kinetic model?
Can you explain evaporation in terms
of the kinetic model?
Thermal Energy Transfer
• From Hot to Cold!
What is thermal equilibrium?
Absolute scale of temperature
What is the advantage
of the absolute
temperature scale?
The Lord!
How do you convert temperatures
measured in Kelvin to degrees
What is the definition of absolute
Thermal Properties of Materials
What is the definition of specific heat
Can you describe an electrical
experiment to determine the specific
heat capacity of a sold or a liquid?
What is meant by the terms
• Latent heat of fusion?
• and.............latent heat of vaporisation?
Ideal Gases
Introducing Robert Boyle
State Boyles Law
Basic assumption used in the kinetic
theory of gases
• A gas consists of a collection of small particles
travelling in straight-line motion and obeying
Newton's Laws.
• The molecules in a gas occupy no volume (that is,
they are points).
• Collisions between molecules are perfectly elastic
(that is, no energy is gained or lost during the
• There are no attractive or repulsive forces
between the molecules.
• How many particles are in a mole?
Introducing Avogadro!
1. What is
2. Can you link
n,N and NA?
Introducing Boltzmann!
Not another
Ideal Gas Equation
Can you
express this in
terms of the
constant, k and
Kinetic Energy of a molecule of a gas
Can you prove this equation?
KE is the mean translational

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