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 1
History Anaximander (610 BC – 546 BC): Apeiron (w/o limit) The Milesian Group: The world is The world is made of made of Water A Single, Key Substance: Water, Fire, Air (Ether), or Thales of Miletus (624 BC - 564 BC): The first philosopher and scientist Soil… Tsou Yen: Taoism Democritus (305 BC – 240 BC) Leucippus Ajivika & Carvaka (460 BC – 370 BC) (5 th Century BC) schools in ancient Anaxagoras India (6 th Century BC) (500 BC - 428 BC) Pluralism Atomism Empedocles (490 BC - 430 BC) History What was Thales really trying to look for? Why a single key substance? Was he simply wrong? Thermodynamics : Why and How does Energy! energy dominate matters (17 th to 18 th Century) Roger Boskovic John Dalton (1745) (1808) Metaphysics: Beyond Physics – The fundamental principles of the universe Issac Newton Science & (1643-1727) Engineering Dmitri Mendeleev Aristotle Antoine (1865) (384 BC - 322 BC) Leibniz (1714): Monad Lavoisier (1777) 2
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 on 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. UC Davis: Chemiwiki http://silenced.co 3
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 ) There are other variables, such as voltage and charges, that can also be taken into • Pressure ( P ) consideration according to necessity. • Volume ( V ) • Internal energy ( U ): Heat – the total thermal energy • Entropy ( S ) – Measure of uncertainty of the system/material configuration S k ln S k P ln P B B i i i 1 For an isolated system in For an isolated system in equilibrium, where P i = 1/ equilibrium, where P i = 1/ k B = Boltzmann Constant = 1.38 10 -23 J/K P i = The probability of the i -th configuration of the system/material = The total number of the possible configurations 4
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