Physics 313

1
Introduction

• Physics 313
• Professor Lee Carkner
• Lecture 1

2
What is Thermodynamics?

• Hot and cold and how they get that way
• Classical Thermodynamics
• Temperature, heat and work can be transformed
  into one another
• Statistical Physics
• The behavior of particles is governed by the laws
  of probability

3
Laws of Thermodynamics

• Zeroth Law
• Temperature always means the same thing
• 1st Law
• Energy is conserved
• 2nd Law
• Randomness always increases
• 3rd Law
• Randomness decreases with decreasing temperature

4
Thermal Equilibrium

• Two objects at different temperatures placed
  together will exchange heat until they are at the
  same temperature
• Zeroth Law
• If A and B are each in thermal equilibrium with T
  then they also are in thermal equilibrium with
  each other

5
Temperature

• For temperature it is best to use the Kelvin
  scale
• TK TC 273.15
• TF (9/5)TC 32
• Temperature is a measure of the random motions of
  the molecules of a substance
• vrms (3RT/M)½
• Kave (3/2)kT
• DEint nCV DT

6
Heat

• Heat is energy transferred between two substances
  as a result of a temperature difference
• The amount of heat needed to change temperature
  is
• Q cm(Tf - Ti)
• The amount of heat needed to change phase is
• Q Lm

7
Work

• Work is the energy change associated with
  expansion or contraction
• W integral p dV
• Work only occurs with a change of volume
• If the volume increases, work is done by the
  system and the work is positive
• If the volume decreases work is done on the
  system and the work is negative

8
Internal Energy

• Internal energy is a measure of the energy of the
  molecules of a substance and depends only on
  temperature
• DEint nCV DT
• CV (3/2)R
• R 8.31 J/mol K

9
First Law of Thermodynamics

• The first law always holds in any situation
• DEint Q - W
• Energy is conserved
• You cannot get more out of a system than you put
  into it

10
Heat Transfer

• Conduction
• H Q/t A(TH-TC) / S (L/k)
• Radiation
• Pr seAT4
• Net power is power received minus power emitted
• Convection
• Hot fluid rises in a gravitational field moving
  heat with it

11
Ideal Gas

• Most gasses can be approximated as ideal gases
• M mNA
• NA 6.02 X 1023 (Avogadros number)
• Ideal Gas Law
• pV nRT
• n (number of moles) and R (gas constant) do not
  change for any given amount of gas

12
First Law and Ideal Gas

• Any ideal gas must obey
• pV nRT
• DEint Q - W DEint n CV DT
• Q n C DT
• W integral p dV

13
Entropy

• High entropy means high randomness
• Entropy always increases
• DS Sf-Si integral dQ/T
• For isothermal processes
• DS Q/T
• First Law output cannot exceed input
• Second Law output cannot equal input

14
Adiabatic

• Definition
• No heat
• pVg, TV(g-1) are constant
• Heat, Work and Internal Energy
• Q 0
• W -DEint -n CV DT

15
Isochoric

• Definition
• Constant volume
• Heat, Work and Internal Energy
• Q DEint n CV DT
• W 0

16
Isothermal

• Definition
• Constant temperature
• Heat, Work and Internal Energy
• Q W nRT ln (Vf/Vi)
• DEint 0

17
Isobaric

• Definition
• Constant pressure
• Heat, Work and Internal Energy
• Q n Cp DT
• W p DV
• DEint n CV DT