Rates

Chemical Reactions only occur when the particles to reactants collide with each other with sufficient enery to cause a reaction

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  • Created by: lollypop
  • Created on: 15-05-13 19:45

Simple Reactions

Chemical reactions can only take place when the particles of the reactant collide with eachother with sufficient energy to cause a reaction. 

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Activation energy

Activation energy is the minimum amount of  energy with which a reactant particles must have to react on collision.

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What Effects the Rate of Reaction:

Temperature: It increases the speed of the collisions, so that they collide more frequently and with greater energy, therefore more sucessful collisions and a faster rate of reaction. (More collisions at or above Ea per second- for every 10'c rise in temperature, there is a doubling in rate)

Concentration: Increases the number of reactant particles per cm3; Therefore the number of collisions per second increases, increasing the rate of reaction (2 x pressure means 2 x more collisions per second which means 2 x rate of reaction) 

Surface area : Increases the possiblility for collisions on the surface of the solid, so increases the rate of reaction (2 x surface area means 2 x more collisions per second which means 2 x rate)

Catylysts: Change the rate of reaction but are not used up in the reaction: they are specific for a particular reaction (i.e the shorter the time, the faster the rate, and the steeper the line (gradient), the faster the rate)

Pressure: Increases the frequency of collisions and so increases the rate of reaction (2 x pressure means 2 x more collisions per second which means 2 x rate of reaction) 

 

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Measuring the rate of reaction

Can be measures by measuring the amount of reactant used up or the amount of product used up over time:

i.e Rate = amount of reactants used/time

or  Rate = amount of product formed/time

Graphs can be created showing the amount of product formed (or reactant used up) against time, in terms of rate (i.e the shorter the time, the faster the rate and the steeper the line (gradient), the faster the rate)

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Catalysts

Catalysts work by providing an alternative pathway for the reaction with the lower Ea 

Catalysts are important in increasing the rates of chemical reactions in industrial processes without increasing temperature, so saving energy and money

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