This preview shows pages 1–3. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: ME 382 Lecture 14 8/ii/06 1 I NTRODUCTION TO K INETICS (I) Reminder ; Atoms & molecules (or other objects) try to minimize Gibbs free energy G = H enthalpy { ! T absolute temperature { S entropy { where, Enthalpy is a generalized form of energy H = U + pV where U includes bond energy, strain energy, atomic concentration, Entropy is a measure of disorder At equilibrium: no force on atoms dG / dx = Away from equilibrium configuration, a force acts to restore equilibrium: F = ! " G " x An external applied force can reestablish equilibrium Otherwise, force results in motion of atoms & molecules to equilibrium configuration Steadystate flow rate (or velocity) mobility x force where mobility is a measure of inverse resistance to motion Analogies: Viscous flow in pipe of radius R : v = ! R 2 8 " dP dx # $ % & Electricity flowing in a resistor: I = A ! dV dx " # $ % ( i.e, I = V / R ) Stokes law (drag force D on sphere of radius a ): v = D /6 "# a ME 382 Lecture 14 8/ii/06 2 Atoms and molecules move by a process known as diffusion Mobility given by the diffusion coefficient (or diffusivity) D = D o exp ! Q / kT ( ) or...
View Full
Document
 Fall '08
 garikipati

Click to edit the document details