Investigating how the concentration of reactants affects the rate of reaction
This experiment is aimed at investigating how the concentration of
reactants affects the rate of reaction:
The reaction between hydrochloric acid and magnesium will be used to
investigate how different concentrations of the acid affect the rate
of reaction. The gas produced from the reaction will be measured and
used to display the average rate of reaction.
The rate of reaction is a measure of how fast a reaction is going and
how long it takes to complete. This rate is found by measuring the
amount of a reactant used up per unit of time or the amount of a
product produced per unit of time. For this reaction, the product will
be measured, as this substance is the easiest and most accurate to
A reaction can be stimulated to go faster or slower by varying the
temperature, the concentration of reactant and the surface area. For
the magnesium and acid particles to react together, they must:
i) Collide with each other
ii) Have enough energy in the collision.
1) The particles in the liquid move around continually. Above, an acid
particle is about to collide with a magnesium atom.
2) If the collision has enough energy, a reaction takes place.
Magnesium chloride and hydrogen will be formed.
3) If the collision does not have enough energy, no reaction occurs
and the acid particle will bounce away again.
Particles need to collide with enough velocity so that they react.
During a chemical reaction, the particles have to collide with enough
energy to first break the bonds and then to form the new bonds and the
rearranged electrons, so some of the particles do not have enough
energy to react when they collide. If many successful collisions occur
in a given minute, then many hydrogen atoms will also be produced in
that minute - The reaction goes quickly, so the rate of reaction is
high. If there are not many collisions, the rate is low. The rate of
reaction depends on how many successful collisions there are in a
given unit of time.
I predict that the 1.0M solution of hydrochloric acid (half the
strength of the original solution) will have the fastest rate of
reaction because it has the highest concentration. I believe this due
to the 'collision theory.' According to this theory, a product can
only be made when there are effective collisions. Simply having
reactant molecules colliding, although necessary, is not sufficient in
itself; the collisions must be effective.
When the acid has a higher concentration, there are more acid
particles moving around, so there is more chance of a successful
I predict that the 0.2M dilution will have the slowest rate of
reaction because it is the weakest solution. In dilute acid, there are
not many acid particles, so there is less chance of an acid particle
hitting a magnesium atom. I also predict that the 0.6M dilution will
have a rate of...