|Factors That Affect Reaction Rates|
|The following are the factors that will affect the rate of a reaction:|
|1. Nature of the Ions Being Used|
|MnO4- added dropwise to
MnO4- added dropwise to
acidified Fe2+ ions acidified C2O42- ions
|The only difference is the nature of the reactants. The ferrous ion
is simple and monatomic while the oxalate ion is polyatomic covalent in nature.
In general reactions between simple ions such as Ag+ and Cl-
which combine in a 1-1 mole ratio, are almost instantaneous. Experimental
measurements show that most of these reactions occur in about 1/1,000,000th
of a second. The nature of the reactants affects the rate of a reaction.
Generally, a more complicated species will react more slowly than a simple
|2. Concentration of Reactants [reactants]|
|The concentration of reactants affects the rate of a chemical reaction
but exactly how will be dealt with in the Iodine-Clock experiment.
|3. Temperature Increases and Decreases|
|The temperature at which an reaction is carried out affects the rate
of a chemical reaction but exactly how will be dealt with in the Iodine-Clock
|Demo: MnO4- and Fe2+
MnO4- + C2O42-
MnO4- + C2O42- + Mn2+
|Substances which affect the reaction rate without being consumed by
the overall reaction are called catalysts. Catalysts may be consumed
during some intermediate step in the reaction and then are regenerated in
a subsequent step.
|Starch, Water & Iodine
Starch, Water, Iodine and Ptyalin
Sugar Cube with Cigarette ash
|5. Surface Area|
|This becomes important in heterogeneous reactions: Heterogenous
reactions are ones that have mixed phases.
eg. Zn(s) + 2 HCl(aq) ----> ZnCl2(aq) + H2(g)
4 Fe(s) + 3 O2(g) ----> 2 Fe2O3(s)
Starch pile Starch powder
As the surface area increases the rate of reaction should also increase. Dust and grain silo explosions are good examples of surface area reactions.