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.