Thermodynamics Notes 13

Thermodynamics Notes 13 - ME 311 FALL 2007 CHAPTER 5...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
ME 311 THERMODYNAMICS S. Masutani FALL 2007 1 CHAPTER 5 (continued) To be able to apply the 2 nd Law in analyses of systems we must be able to evaluate entropy as a function of state. 2 ways: 1. Determine the probabilities of energy microstates and apply the results of quantum– statistical mechanics to evaluate S from spectroscopic and other data on the molecules of the system. 2. Determine entropy from macroscopic laboratory data (averaged over many molecules and molecular events over a “long” period of time–relative to the molecular timescales), utilizing relationships between S and other thermodynamic variables which can be evaluated directly. The Statistical Definition of Entropy (modern) (non-rigorous derivation) The underlying concept in our pursuit of a formulation for entropy is that the total energy of a system under study, i.e., a quantity of matter, is the sum of the energy retained by each of the constituent molecules (or atoms). In a classical description, each particle is described by continuous position coordinates and corresponding momenta. Energy appears as a continuous function of these variables (position; momenta). Entropy reflects our uncertainty about the distribution of the molecules of the system in this position–momentum space. Quantum mechanics has shown that, at the microscopic level, matter exists only in discreet quantum states. Statistical thermodynamics has incorporated this “new” understanding into its established framework: the total energy, E, of a system corresponds to some distribution of N particles among the permissible energy states ε 1 , ε 2 , …, ε i ,….
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 5

Thermodynamics Notes 13 - ME 311 FALL 2007 CHAPTER 5...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online