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Collision Theory and Reaction Rates
Transcript of Collision Theory and Reaction Rates
particles must collide in order to react
concentration of reactants
surface area of solid reactants
Increased concentration causes higher collision frequency.
collision must have more energy than the activation energy, Ea
molecules must collide in the correct orientation
Increased pressure causes higher collision frequency for gases.
Increased surface area means increased number of particles exposed, therefore collision frequency is higher.
Average kinetic energy is proportional to temperature. Hence, increased temperature means increased speed of particles and more collisions.
At higher temperature there are more particles with energy greater than or equal to the activation energy. Hence, More collisions are effective.
Catalysis allows an alternative reaction pathway with a lower activation energy.
Rate = change / time For chemical reactions -rate = how fast the concentration of a reactant or product changes with time.
Write the reaction rates in terms of each product and reactant
Rates and rate laws are determined experimentally.
You cannot look at a reaction and know what the rate law is.
Integrated Rate Laws
How many collisions per second for typical reactions?
Nitrogen and oxygen collide 10^27 times per second at RT and 1 atm! Clearly the collisions don't all lead to NO, or we'd suffocate! Hydrogen and iodine collide 10^10 times per second.
Reaction Diagrams or Reaction Coordinates
Endothermic vs Exothermic
Transition States and Intermediates
Imagine the reactions are reversed. Rate the reverse reactions from slowest to fastest.