Kinetics: Rate of Reactions

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Information about Kinetics: Rate of Reactions

Published on February 7, 2009

Author: suef


Slide 1: Collision Theory NO3 + CO ? NO2 + CO2 Slide 2: Molecules bounce (no reaction) Reactants not facing the right way (wrong orientation) Collision Theory NO3 + CO ? NO2 + CO2 Slide 3: Collision Theory NO3 + CO ? NO2 + CO2 Slide 4: Collision Theory NO3 + CO ? NO2 + CO2 Slide 5: Activation Energy Energy needed to be put into a reaction (to break bonds) before the products can be produced. Slide 6: Effect of Concentration = successful collision Slide 7: Effect of Concentration Note the number of moles of product is the same Slide 8: Effect of Surface Area Area in contact with reactant (big block = small SA) Slide 9: Effect of Surface Area Slide 10: Effect of Increased Volume of Solution Solution + Solid = no change in rate Increasing volume has no effect on concentration, so frequency of collisions remains constant If solution is the limiting reagent, an increase in volume will increase the amount of product formed Solution + Solution = increase in rate Doubling the volume of solution A results in an increase in concentration of red particles per unit volume – rate will increase Slide 11: The particles with high kinetic energy can successfully react. Effect of Temperature Fraction of Molecules having a certain Kinetic Energy Slide 12: Activation energy for reaction Effect of Temperature Slide 13: Effect of Temperature Slide 14: Effect of Catalysts Catalyst – remains unchanged at end of reaction (can be used over and over again) Reactant Product Catalysts speed up reactions Slide 15: Effect of Catalysts = Lower Activation Energy Without a catalyst: lots of energy is needed to go over the hill Slide 16: Effect of Catalysts = Lower Activation Energy More particles have the necessary kinetic energy to have a successful reaction = increased rate Slide 17: Reaction Mechanisms Most reactions have more than one step to form the products. Even reactions with simple stoichiometry usually have a multi-step reaction mechanism. No matter how fast the other steps are, the overall rate of the reaction will only go as fast as the rate of the slowest step. The slowest step is called the rate determining step. Slide 18: Multi-Step Reactions If three or more reactants need to collide in a reaction, definitely more than 1 step will be needed: The probability of more than 2 reactants colliding with enough energy & in the right orientation at the same time for a successful reaction is very low. Doesn’t happen Actual mechanism: 2 steps Slide 19: In multi-step reactions, each step will have it’s own activation energy and therefore its own rate. The SLOWEST step determines how fast the whole reaction can go. The slowest step is called the rate determining step of the reaction Slide 20: Interactive Concepts in Biochemistry - Interactive Animations The following address has a good interactive animation on catalysis.

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