Entropy Second Law

ENTROPY AND THE SECOND LAW OF THERMODYNAMICS

Energy Reservoir

The system consists of the red circles in the blue box.

Energy and entropy flow out of the system. Additional Energy is added to the system, TIME

The system decreases in entropy

by DR. STEPHEN THOMPSON MR. JOE STALEY

The contents of this module were developed under grant award # P116B-001338 from the Fund for theImprovement of Postsecondary Education (FIPSE), United States Department of Education. However, those contents do not necessarily represent the policy of FIPSE and the Department of Education, and you should not assume endorsement by the Federal government.

ENTROPY AND THE SECOND LAW OF THERMODYNAMICS CONTENTS
2 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Introduction To Entropy EnergyDisperses Entropy Enthalpy And Entropy Thermal Entropy Configurational Entropy Configurational Entropy: Cellular Representation Configurational Entropy: Combined Representation Dispersible Energy Diffusion Liquid Crystal Salt Dissolving In Water The Pfeffer Tube The Second Law Of Thermodynamics Gibbs Free Energy Gibbs Free Energy And Temperature Gibbs Free Energy And Temperature How Entropy Can Decrease(In A System) Periodic Entropy Of The Elements

ENTROPY AND THE SECOND LAW OF THERMODYNAMICS INTRODUCTION TO ENTROPY ENERGY DISPERSES

Metal Time

Styrofoam Time

TIME

Time

Time

Time

Time In the picture above the red ink represents energy. As time proceeds there is the same amount of ink (energy) but it spreads out, becomes less concentrated, disperses. Entropy is the measureof this dispersal The second law of thermodynamics says that the opposite change is impossible in an isolated system.

In the experiments pictured above, the blue represents cooling, or loss of thermal energy. Is the evaporation of water exothermic or endothermic.? What is the evidence? If it is endothermic, how can it proceed spontaneously in the isolated system where the petri dish is placed onstyrofoam? Spontaneous endothermic reactions do occur and that means that there must be another factor than enthalpy involved. Scientists call this factor entropy.

We have personal experience of entropy when we feel the coolness of evaporation.

2

ENTROPY AND THE SECOND LAW OF THERMODYNAMICS ENTROPY
Suppose three molecules have a total of three quanta of energy to share between them andthat each molecule can occupy one of four energy states requiring zero, one, two or three quanta to occupy. E3 E2 x y z E1 o o o E0 Macrostate 1 has one possibility, that is, one microstate. E3 z E2 y o E1 x o E0 o E3 o E2 E1 y z oo E0
x

o o
x

y

o o
z

z

oo

x y

Macrostate 2 has three possibilities, that is, three microstates.

oz o o z o x x o o y o o z x y o o o oMacrostate 3 has six possibilities, six microstates.

y

z

x

y

oy oz o

x

In chemistry there are several different means by which energy can be dispersed and thus entropy created. These include: 1. The number of molecules among which the entropy can be shared. The rest of these examples refer to the same number of molecules: 2. The volume of space which the molecules can occupy. 3. Thefreedom with which the molecules can move about that space, e.g, the difference between a solid and a liquid. This would include the freedom to change location and, in the case of nonspherical molecules, the freedom to change oritentation or rotation. 4. The amount of energy available, which determines the range of energy states which the molecules can occupy. 5. The complexity of the molecules,which determines how many rotational and vibrational states they can have. A modern way to describe entropy is to say that entropy increases with the number of ways energy can be distributed in a system.

Suppose each microstate is as likely to be occupied as any other microstate. What is the most likely macrostate to be occupied? Suppose that the system shifts from one microstate to another...