"Experiment is the interpreter of nature.
Experiments never deceive. It is our judgment
which sometimes deceives itself because it
expects results which experiment refuses."
- Leonardo da Vinci
(1452-1519)
Thermodynamics
• Large number of particles ~
N
= 6.022  1023 = mole (the quantity of matter that contains
as many identical objects [e.g. atoms, molecules, formula units,
ions] as the number of atoms in exactly 12 g of 12C)
A
• Fluctuations are small and can
often be ignored, i.e.,
the thermo-dynamic limit
F  d (mv ) / dt
Thermodynamic limit
Pressure, Volume, Temperature
P, V, T
F/A
L3
Something to
do with heat
What is heat ?
Heat is energy in transit !
Surroundings
System
Heat
Universe =
(system +
surroundings)
Heat is measured in Joules
What is temperature?
Temperature is what you measure with a thermometer
Temperature is the thing that’s the same for two
objects, after they’ve been in contact long enough.
Long enough so that the two objects are in thermal
equilibrium.
Time required to reach thermal equilibrium is the
relaxation time.
Temperature is usually measured in K, C or F and
cannot be expressed in mechanical units (mass, length
and time).
Temperature is a measure of the tendency
of an object to spontaneously give
up/absorb energy to/from its surroundings.
Diathermal wall is a system boundary that freely
allows heat to be exchanged, i.e. very short relaxation
time for systems separated by a diathermal wall.
Adiabatic wall is a system boundary that does not
allow heat to be exchanged, i.e. very long relaxation
time for systems separated by a adiabaric wall.
T 1- T 2
T 1- T 2
Adiabatic wall
time
time
VG-8
Ideal gas equation of state
Boyle’s law
p  1/V
Robert Boyle (1627 – 1691)
Charles’ law
pV = NkB T
VT
Jacques Charles (1746 – 1823)
Gay-Lussac’ law
kB = 1.38  10-23 J/K
pT
Joseph Louis Gay-Lussac (1778 - 1850)
VG - 9
How much “energy in transit” needed to
raise temperature of an object by dT ?
Heat capacity (units JK -1)
dQ
C
dT
 Q 
CV  

 T V
 Q 
CP  

 T  P
Specific heat capacity (c) is the
heat capacity per unit mass.
Specific heat of a solid
Copper
Measurement of heat capacity by relaxation calorimetry
Thermometer needs to have a much lower heat capacity
than the sample
T
T0 + T
T0 + T
T0
T0
Heater
Sample
Thermometer
t