Thermodynamics
System / environment
Diathermal / adiabatic
Walls between the system and surroundings are called diathermal if they permit energy flow in or out
Diathermal / adiabatic
Adiabatic walls do not permit any energy flow (perfect insulators)
Q, W, UHEATWORK
INTERNAL ENERGY
Ways to change U
ΔUQ
W
Energy added as heat can be used to do work
Q ΔU W
Energy added through work can be released as heat
QΔUW
Laws of TD
• 1) You can’t win.• 2) You can’t break even.• 3) You can’t quit.
0’th Law
• Energy flows from an object with a higher T to the object with a lower T…
NATURALLY
First Law of Thermodynamics
QU W You can’t win… energy does not just ‘come out of nowhere’
Isobaric process: P = const
Isobaric graph
Amount of work done
Example 1
3 “ISOS-” and “ADIA-”• Isobaric – a thermodynamic process that takes
place at a constant pressure• Isochoric – a thermodynamic process that
takes place at a constant volume• Isothermal - a thermodynamic process that
take place at a constant temperature• Adiabatic - a thermodynamic process in which
Q = 0
Isochoric graph
Isochoric
Isothermal
Isothermal
Adiabatic
Adiabatic
Thermodynamic processes:
• Isothermal T = const ΔU• Isochoric V = const W • Adiabatic Q• Isobaric P=const
Isochoric process
1st Law of Thermodynamics
Isothermal
1st Law of Thermodynamics
Note : in case of phase change internal energy changes even if temperature does not.
Adiabatic
1st Law of Thermodynamics
Isolated system
NO CHANGE IN INTERNAL ENERGY
Heat Engine
Step 1 – intake
Step 2 – compression. U is increased by work done on the mixture
Power / work step –due to combustion the gasis doing work pushingthe piston down.
Exhaust – gas (and the ‘left over’ energy) is pushed out)
Efficiency of a Carnot Engine
a) U increases through heat
b) U increases through work
c) U decreases through heat
d) U decreases through work
2nd Law of Thermodynamics
2nd Law of ThermodynamicsEntropy – the measure of a system’s disorder
2nd Law: All natural processes lead to increase of entropy of the universe.
3rd Law of Thermodynamics
It is not possible to lower the temperature of any system to absolute zero.
