Outline History of Thermodynamics: From Metaphysics to Science - - PDF document

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A Brief Introduction to Thermodynamics

Professor Yu Qiao University of California, San Diego

9500 Gilman Dr. MC 0085, La Jolla, CA 92093-0085 Phone: 858-534-3388  Email: yqiao@ucsd.edu

Outline

• History of Thermodynamics:

From Metaphysics to Science

• Basic Concept:

Energy Conservation and Entropy

• System Behaviors:

Most Energetically Favorable Configurations

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History

Thales of Miletus (624 BC - 564 BC): The first philosopher and scientist

The world is made of Water The Milesian Group: The world is made of A Single, Key Substance: Water, Fire, Air (Ether), or Soil…

Anaxagoras (500 BC - 428 BC) Empedocles (490 BC - 430 BC)

Pluralism

Tsou Yen: Taoism (305 BC – 240 BC) Ajivika & Carvaka schools in ancient India (6th Century BC) Leucippus (5th Century BC) Democritus (460 BC – 370 BC)

Atomism

Anaximander (610 BC – 546 BC): Apeiron (w/o limit)

History

Aristotle (384 BC - 322 BC)

Metaphysics: Beyond Physics – The fundamental principles

• f the universe

Science & Engineering

Antoine Lavoisier (1777) Dmitri Mendeleev (1865) John Dalton (1808) Leibniz (1714): Monad

What was Thales really trying to look for? Why a single key substance? Was he simply wrong?

Energy!

(17th to 18th Century)

Thermodynamics:

Why and How does energy dominate matters

Roger Boskovic (1745) Issac Newton (1643-1727)

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Basic Concept

Zero-th Law: If two systems are each in thermal equilibrium with a third, they are also in thermal equilibrium with each other. First Law: A change in the internal energy of a closed thermodynamic system is equal to the difference between the heat supplied to the system and the amount of work done by the system

• n its surroundings.

Energy Conservation! Energy flows

(wordpress.com)

Basic Concept

• Second Law: Heat cannot spontaneously flow from a colder location to a

hotter location.  Energy flow is one-way, irreversible (so does time!)  Always along the direction to maximize entropy  Perpetual motion machines do not exist

• Third Law: As a system approaches absolute zero, all processes cease

and the entropy of the system approaches a minimum value. http://silenced.co UC Davis: Chemiwiki

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Basic Concept

• The probability for a system/material to increase entropy is always higher

than to decrease entropy

• For example, consider a number of hard beads being shaken in a box:

Scenario A: all the beads distribute uniformly Scenario B: the beads only distribute in one side of the box, leaving the other half empty Both Scenarios A & B have the same internal energy, but A has a higher entropy (the number of possible arrangements of the beads is larger). Thus, the system configuration tends to leave B and stay at A.

• The beads are analogues to the air molecules in a room.

Marek Straszak DonnaBellas.com AlexB17

System Variables

A number of variables are used to characterize a system/material:

• Temperature (T)
• Pressure (P)
• Volume (V)
• Internal energy (U): Heat – the total thermal energy
• Entropy (S) – Measure of uncertainty of the system/material configuration



 

 

1

ln

i i i B

P P k S

  ln

B

k S

For an isolated system in equilibrium, where Pi = 1/ For an isolated system in equilibrium, where Pi = 1/ kB = Boltzmann Constant = 1.3810-23 J/K Pi = The probability of the i-th configuration of the system/material  = The total number of the possible configurations There are other variables, such as voltage and charges, that can also be taken into consideration according to necessity.