Editing Kinetics

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==Rates of Reaction==
*A '''rate of reaction''' for a certain reaction is defined as
**the rate of '''decrease''' in concentration of one of the ''reactants'' per unit time, or 
**the rate of '''increase''' in concentration of one of the ''products'' per unit time.
***Rates of reaction are therefore measured in mol dm^(-3) s^(-1)
The gradient on a concentration/time graph for a reactant or product involved in a reaction is equal to the rate of reaction. You should be familiar with what these graphs look like -- it is likely that they will show up on the test.

==Collision Theory==
molecules can react with one another when:
*they hit each other:
**with the correct collision geometry (the reactive parts get close enough each other to react)
**and with the required '''activation energy''' for that particular reaction

==Factors that can change the rate of reaction==
===Concentration===
If there are more molecules in a fixed space, they will collide more often.
*Therefore the rate of reaction will increase with a higher concentration of reactants

===Surface area===
If the reactants have a higher surface area (eg. they are cut into small pieces) they will have a larger area to react with.
*Therefore the rate of reaction will increase if the reactants have a higher surface area.
**eg. thin sawdust can practically explode, but wood only burns. Why is this?

===Temperature===
If the molecules have more kinetic energy, they will:
#Collide more often
#Be more likely to possess the required activation energy for the reaction
*Therefore the rate of reaction will increase at higher temperatures

===Catalysts===
A catalyst can provide an alternate reaction path with lower activation energy or fewer steps. Catalysts are involved in the reaction, but are returned to their original state afterwards.
*If a reaction with lower activation energy is possible, more molecules will have the required activation energy, so more molecules will react quickly.
**Therefore the presence of a catalyst can increase the rate of reaction.

==Rate-determining step==
Reactions normally occur in more than one step, for example, the reaction: 

 A + B + C -> D + E 

may actually happen as a series of reactions:
# B + C -> D + F (B and C turn into D and F)
# F + A -> E (the F that has been formed combines with A to form an E)
*Each of these smaller reactions have their own rate.
**All of the smaller reactions have to be completed for the whole one to be completed.
**The '''rate-defining step''' is the one with the slowest rate.

[[Category:Chemistry]]