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9-23-09_kinetics1

# 9-23-09_kinetics1 - Tick Well once again my friend we find...

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Tick : Well, once again, my friend, we find that science is a two-headed beast. One head is nice, it gives us aspirin and other modern conveniences... But the other head of science is bad. Oh, beware the other head of science, Arthur. It bites

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Announcements Quiz 3 available Friday. Due Wednesday by noon. Extra credit assignments: Attend and report on research seminars. Worth 3 points on an exam. Can get credit for up to 3 seminars. Seminar must be clearly related to biology. Guidelines for report posted on Blackboard. Submit report on Blackboard in “Assignments”. Up to 3 reports can be submitted over course of semester.
Other formulations of entropy give insight into how to think about entropy Boltzmann entropy, S=k B ln Ω , where k B is Boltzmann’s constant and Ω is the number of microstates in the system Gibb’s entropy, S=-k B Σ i p i ln p i , where pi is the probability of being in the ith microstate. P(E i )=(1/Z) e -E i /k B T , where P(E i ) is the probability of having a microstate with energy E i , 1/Z normalizes the probability Shannon entropy, or information entropy, H= -Σ i p i log 2 p i . This is identical to Gibb’s entropy except for scaling by a constant. Shared pain is lessened; shared joy is increased; thus do we refute entropy – Spider Robinson

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What does all this entropy have to do with biology? Gibb’s free energy ΔG=ΔH-TΔS , where G is the Gibb’s free energy, H is enthalpy Reactions and other events occur spontaneously when they go from a higher energy state to a lower energy state, or ΔG<0 . ΔG is considered a change in useful energy, and TΔS is considered energy unavailable for further work. Spontaneous reactions occur without any addition of energy and are exergonic or exothermic. Those requiring energy for the reaction to occur are endergonic or endothermic. Despite a reaction occurring spontaneously, no idea what rate of reaction is
The reaction quotient Q, gives the current state of the products and reactants For the reaction A+B ↔ C+D The equilibrium constant Keq=k1/k2= [C][D]/ [A][B] Δ = -RT ln Keq or -1.4 log Keq For the reaction A+B ↔ C+D, Q=[C][D]/[A][B] is the reaction quotient.

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