IB Chemistry/Kinetics
Rates of reaction
7.1.1 : Rate of reaction is concerned with how quickly a reaction reaches a certain point (not to be confused with how far a reaction goes...i.e. equilibrium).
7.1.2 : Interpretation of rate graphs. Reaction rate graphs will generally be graphed with time on the x-axis and some measure of how far the reaction has gone (ie concentration, volume, mass loss etc) on the y-axis. This will generally produce a curve with, for example, the concentration of the reactants approaching zero.
Collision theory
7.2.1 : Collision theory -- reactions take place as a result of particles (atoms or molecules) colliding and then undergoing a reaction. Not all collisions cause reaction, however, even in a system where the reaction is spontaneous. The particles must have sufficient kinetic energy, and the correct orientation with respect to each other for the two to react. Even then, the transition state may revert to the reactant molecules instead of forming the product molecules.
7.2.2 : Higher temperature causes a greater average kinetic energy of the particles in a material. This leads to a faster reaction because there are more collisions, and each collision is more likely to succeed.
Higher concentrations cause more collisions and therefore a faster reaction.
Catalysts may provide an alternative pathway with lower activation energy and increase the probability of proper orientation. Each collision is more likely to succeed and this results in a faster reaction.
In heterogeneous reactions (where the reactants are in different states) the size of the particles of a solid may change reaction rate, since the surface is where the reaction takes place, and the surface area is increased when the particles are more finely divided; therefore smaller solid particles in a heterogeneous reaction cause a faster reaction.
7.2.3 : Most reactions involve several steps, which can be individually slow or fast, and which, all together, make up the complete reaction. The slowest of these steps is called the rate determining step, as is determines how fast the reaction will go. It is also not necessary that all the reactants are involved in ever step, and so the rate determining step may not involve all the reactants. as a result, increasing their concentration (for example) of a reactant which is not involved in the rate determining step will not change the overall reaction rate.
[edit] HL Material
Topic 16 is the additional HL material for Topic 7.
Activation energy
