thermodynamics
DESCRIPTION
"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). - PowerPoint PPT PresentationTRANSCRIPT
"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 ~ NA = 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)
• Fluctuations are small and can often be ignored, i.e., the thermo-dynamic limit
( ) /F d mv dt
Thermodynamic limit
P, V, T
Pressure, Volume, Temperature
F/A L3 Something to do with heat
SystemSystem
SurroundingsSurroundings
HeatHeat
Universe = Universe = (system + (system + surroundings)surroundings)
Heat is energy in transit !
What is heat ?
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.
T1- T2
time
T1- T2
time
Adiabatic 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.
VG-8
Ideal gas equation of state
Robert Boyle (1627 – 1691)
Boyle’s law
p 1/V
Jacques Charles (1746 – 1823)
Charles’ law
V T
Joseph Louis Gay-Lussac (1778 - 1850)
Gay-Lussac’ law
p T
pV = NkB T
kB = 1.38 10-23 J/K
VG - 9
How much “energy in transit” needed to raise temperature of an object by dT ?
Heat capacity (units JK-1)
dT
dQC
VV T
QC
PP T
QC
Specific heat capacity (c) is the heat capacity per unit mass.
Specific heat of a solidSpecific heat of a solid
Copper
Thermometer needs to have a much lower heat capacity than the sample
SampleHeater Thermometer
T0
T0 + T
T
t
T0 + T
T0
Measurement of heat capacity by relaxation calorimetry