Factors That Affect the
Rate of a Reaction
“So…A little heat
and some of my new,
super-effective catalyst
and the Pumpkinator 7000
is…Oh my God…”
What is a Chemical Reaction?
A chemical reaction occurs when the particles of the
reactants collide with one another and stick together in
new combinations to create new substances – these are
the products.
When the particles of the reactants strike one another
and form a new substance, we can look at this as a
“meaningful collision” – it gave us some product.
We can manipulate/control several factors related to
chemical reactions that will help us speed them up and
get more product at a quicker pace.
Before we examine these factors, we must look at the
particles themselves and see how they behave and
interact.
The Fast & the Furious
The nature of particles is addressed in what is known
as the Particle Theory or, as it is also known, the
Kinetic Molecular Theory (KMT).
This theory has several simple points that discuss
what matter really is and how the particles that make
up matter really behave.
1. All matter is made of tiny particles that are constantly
moving.
2. The particles’ speed depends on the amount of energy they
possess. The greater the energy; the greater the speed.
3. The particles will move in a straight line until it strikes
another particle. It will then bounce off of this particle and
continue to move in a straight line, but in a new direction.
Particles & State
This illustration shows how the particles act in
each of the three states of matter.
SOLID LIQUID GAS
A Real Smash Hit!
When we see how the particles of a substance actually behave, we
can then start to control this behaviour and get a chemical reaction
to occur much quicker.
To get a reaction to proceed at a quicker pace, we must get the
particles involved to get into more of those “meaningful
collisions” – we are talking about the high-impact type!
The four factors that we can use to affect the rate of a chemical
reaction are:
1. Temperature
2. Concentration
3. Surface Area
4. Catalysts
These factors will help us by doing one of two things:
speed up the particles and make the collisions more violent (and
meaningful at the same time)
increase the number of collisions overall and this should give
us more meaningful type as well.
Turning Up the Heat!
The term “temperature” is used to indicate the
amount of heat energy an object has.
As you add more heat to an object, the particles of the
reactants absorb this heat and start moving faster and
faster. This makes the collisions between the particles
much more violent and meaningful – the formation of
product will increase quickly.
So…As temperature increase; reaction rate increases.
Examples:
Using a Bunsen burner to heat a test tube in a lab.
Baking a cake in an oven.
“Made From Concentrate”
Concentration is the number of particles in a given
volume of space.
As you increase the concentration of substance, you are
increasing the number of particles in the reaction. This
means that you will have a higher number of collisions
and a greater chance that some of those collisions will
be the “meaningful” type.
So…As concentration increases; the reaction rate
increases as well.
Examples:
Using a more concentrated acid to etch some glass.
Adding more octane to gasoline to burn more efficiently.
Chemicals Exposing Themselves?!?!
Surface area is the amount of a substance that is exposed to the
outer environment.
When substances are going to react with one another, they have
to collide and this means that the surface of one substance must
fit the surface of the other substance.
The more surface area a substance has exposed; the more
particles are exposed to and are able to react with other particles.
You are now able to have more collisions taking place – more
collisions means more chances of “meaningful collisions” taking
place.
So…As more surface area is exposed on a substance; the faster
the rate of reaction
Examples:
Grinding up a metal block into powder for a reaction.
Using wood chips and kindling to start a fire.
Catalysts
A catalyst is a substance that increases the rate of a reaction by
lowering the activation energy required by the reaction.
The activation energy is the amount of energy that a reaction
needs to get started. It’s like the spark needed to get a can a
gasoline to explode.
A catalyst helps turn the reactants into products without
becoming a product in the reaction – it is not consumed in the
reaction like a fuel.
There are biological catalysts called enzymes that allow the
reactions in your body to proceed without consuming too much
of your energy.
So…The rate of reaction is quicker when a catalyst is used.
Examples:
Digestive enzymes in your body breaking down your food.
A catalytic converter in a car breaking apart the contaminants in exhaust.
THE END