Lecture14 - ME 382 Lecture 14 8/ii/06 1 I NTRODUCTION TO K...

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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 re-establish equilibrium Otherwise, force results in motion of atoms & molecules to equilibrium configuration Steady-state 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...
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Lecture14 - ME 382 Lecture 14 8/ii/06 1 I NTRODUCTION TO K...

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