Gas Laws & Absolute Zero
Thermal Physics Lesson 3
Learning Objectives
State the three gas laws, describing the
relationships between p,V,T and mass.
Describe how the thermodynamic scale is
defined.
Define absolute zero.
Convert temperatures between Celsius and
Kelvin.
Thermodynamic Temperature
Scale
A change of 1 K equals a change of 1 oC.
To convert from degrees Celcius into kelvin add
273.15:-
K  C  273.15
Definition
Absolute Zero is the lowest possible
temperature, and something at this temperature
has the lowest possible internal energy.
This is zero kelvin, written 0 K, on the
thermodynamic temperature scale.
Definition
The internal energy of an object is the sum of
the random distribution of the kinetic and
potential energies of its molecules.
Boyle’s Law
Temperature and moles of gas are constant
Graph is hyperbolic (see below) and
asymptotic to both axes
Pressure and volume are inversely
proportional to each other
1
p
V
Ideal Gas vs. Perfect Gas
Strictly speaking an ideal gas is one that obeys
Boyle’s law with complete precision.
A perfect gas is a real gas under conditions that
Boyle’s law is a valid enough description of its
behaviour.
Charles’ Law
Pressure and moles of gas are constant
Graph is linear (see right)
Volume and temperature are directly
proportional to each other
V T
Pressure Law (Gay-Lussac's Law )
Volume and moles of gas are
constant
Graph is linear (see right)
Pressure and temperature are directly
proportional to each other
p T