scotty 12 - Chemistry 13 Part 2 13.5: The Effect of...

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Chemistry 13 Part 2 13.5: The Effect of Temperature on Reaction Rate The rates of chemical reactions are, in general, highly sensitive to temperature. A temperature increase generally results in an increase in k, which results in a faster rate. The modern form of the Arrhenius equation relates the rate constant (k) and the temperature in Kelvins (T) o K = Ae -Ea/RT The activation energy (E a ) is an energy barrier or hump that must be surmounted for the reactants to be transformed into products. o In 13.13, notice to get from the reactant to the product, the molecule must go through a high-energy intermediate state called the activated complex, or transition state. o Even though the overall reaction is energetically downhill (exothermic), it must first go uphill to reach the activated complex because energy is required to initially weaken the bonds. o The energy required to create the activated complex is the activation energy. The higher the activation energy, the slower the reaction rate (at a given temperature). The frequency factor (A) represents the number of times that the reactants approach the activation barrier per unit time. o The frequency factor represents the rate at which the reactant molecule vibrates (or rocks back and forth). With each vibration, the reactant approaches the activation barrier. However, approaching the barrier is not equivalent to surmounting it. Most approaches do not have enough total energy to make it over the barrier. The exponential factor is a number between 0 and 1 that represents the fraction of
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This note was uploaded on 04/01/2011 for the course CHEMISTRY 2400 taught by Professor Staff during the Fall '10 term at Georgia State University, Atlanta.

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scotty 12 - Chemistry 13 Part 2 13.5: The Effect of...

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