SCH4U Rates of Reaction: Factors That Affect Reaction Rates

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

Demonstration:

MnO₄^-added dropwise to MnO₄^-added dropwise to
acidified Fe²⁺ ions acidified C₂O₄^2-ions

Results: Results:

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 1/1,000,000^th 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 ion.

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 experiment.

4. Catalysts

Demo: MnO₄^-and Fe²⁺ MnO₄^- + C₂O₄^2- MnO₄^-+ C₂O₄^2- + Mn²⁺ ions

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 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.