Teachit-rates-of-reaction

Rates of reaction

Information sheet one – measuring rates

The rate of a chemical reaction tells us how fast reactants are
turned into products.

Knowing and In the body chemical
controlling the rate reactions must take
of reactions is place at the correct rate
important in living to supply your cells with
cells and industry. exactly what they need
when they need it.

The products of
chemical reactions
make money so it is
important to be able to
speed up the rate and
make them as cheaply
as possible.

The rate of some reactions is very fast, like a firework exploding.
The rate of some reactions is very slow, like a car rusting.

There are two There are three main ways to take these measurements.
ways we can
measure the rate We can measure the If a gas is one of the Some reactions
of a chemical volume of gas given products we can make the solution go
reaction. off in a certain measure the cloudy. We can
amount of time. decrease in mass measure the amount
• Measure during a reaction as of light they allow
how quickly the gas is given off. through. This will
the decrease as the
reactants reaction goes on.
are used
up.

• Measure
the rate at
which the
products
are made.

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Rates of reaction

Information sheet two – collision theory

There are four main factors that affect the rate of chemical reactions:
surface area, catalysts, temperature and concentration (liquids) / pressure
(gases).

Reactions can only take a) A collision without
place when the particles enough energy means
that make up the
reactants come that there is no
together. The particles reaction.
cannot just bump into
each other they must A collision with enough
collide with enough energy means that
energy to react. This is
collision theory. there will be a reaction.

b)

Activation energy

The smallest amount of energy that particles must have before they react is called the
activation energy.

Speeding up reactions

Anything that increases the chance of reacting particles colliding with each other or
increases the amount of energy they have when they collide will make it more likely for a
reaction to happen and the rate of reaction to increase.

For two particles to react …. …. they must first collide.
Two particles will only react …. … if they have enough energy.
The energy required for particles to react … is called the activation energy.

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Rates of reaction

Information sheet three – effect of temperature

Increasing the temperature of a
reaction always increases the rate of
reaction. Collision theory tells us why
this happens.

When we heat up a substance energy gets transferred to the particles of the
substance. This means they move faster and will have more collisions.

Every time the particles collide they do so with more energy. This means that
there are more successful collisions and the rate of reaction increases.

Low temperature High temperature
slow movement fast movement
few collisions lots of collisions
low energy high energy

The 10 ˚C rule For every 10 ˚C temperature increase the
rate of reaction doubles.

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Rates of reaction

Information sheet four – effect of concentration

Increasing the concentration of the
reactants in a solution increases the
rate of the reaction.

Increasing the concentration of reactants in a solution increases the number
of particles moving around in the same volume. The more crowded they are
the more collisions occur and the rate of reaction increases.

Increasing the pressure of a reaction involving gases has the same effect as
increasing the concentration. The gas particles become pushed closer
together and so they collide and react more often.

Low concentration High concentration
= few collisions = more collisions

Remember:
higher concentration = more particles = more collisions

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Rates of reaction

Information sheet five – effect of surface area

Increasing the surface area of a
solid reactant increases the rate
of reaction.

If one of the reactants is solid it can be broken up into smaller
pieces. This increases the surface area for the other reactant to
collide with.

Increasing the surface area increases the number of collisions
between reactants. Increasing the collisions increases the rate of
reaction.

Small surface area Large surface area

Remember

Smaller particles = bigger surface area = more collisions

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Rates of reaction

Information sheet six – effect of a catalyst

Adding a special substance called a
catalyst speeds up the rate of the
reaction.

The catalyst itself does not take part in the reaction as a reactant. It
is not changed by the reaction and it is not used up during the
reaction. It is still there in the same form when the reaction is
complete.

A catalyst works by providing a surface for the reaction to occur.

The particles involved in the reaction gather on the catalysts
surface allowing them to:
1) collide more often
2) have a lower activation energy.

Different reactions have different catalysts.

Catalysts are often very expensive as they are precious metals.

Remember

Use of a catalyst = more collisions and a lower activation
energy

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Rates of reaction

Information sheet one – measuring rates

1. What does the rate of reaction tell us?

2. Why is controlling the rate of reaction important in the body?

3. Why is the rate of reaction important in industry?

4. What are the two ways we can measure the rate of reaction?
i)
ii)

5. What are the three ways we could take these measurements?
i)
ii)
iii)

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Information sheet two – collision theory

1. What are the four main factors that affect the rate of reaction?
i)
ii)
iii)
iv)

2. What does collision theory tell us about what needs to happen for a reaction can
take place?

3. What is activation energy?
4. Draw a diagram to show collision theory.

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Rates of reaction

Information sheet three – effect of temperature

1. What effect does increasing temperature have on the rate of reaction?

2. Why does temperature increase the rate of reaction?

3. Draw a diagram that shows the effect of increasing temperature on reacting
particles.

low temperature high temperature
4. What is the 10 ˚C rule?

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Information sheet four – effect of concentration

1. What effect does increasing concentration have on the rate of reaction?

2. Why does an increase in concentration increase the rate of reaction?

3. Draw a diagram that shows the effect of increasing concentration on reacting
particles.

low concentration high concentration

4. Explain why increasing the pressure in gases increases their rate of reaction?

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Rates of reaction

Information sheet five – effect of surface area

1. What effect does increasing the surface area of reactants have on the rate of
reaction?

2. Explain why increasing surface area increases the rate of reaction.

3. Draw a diagram to show the effect of increasing surface area on reacting particles.

low surface area high surface area

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Information sheet six – effect of a catalyst

1. What effect does adding a catalyst have on the rate of reaction?

2. What happens to a catalyst during the reaction?
i)
ii)

3. Why does a catalyst increase the rate of reaction?
i)
ii)

4. Can a substance that is a catalyst be used to speed up any reaction?

5. Why are catalysts often expensive?

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Rates of reaction
Teaching notes

This resource is suitable as a revision exercise. It can be used in a variety of ways.

• Set up six ‘Information stations’ around the room. Number the stations and put
several copies of the corresponding information sheets at each station. They could
be taped down onto the table. Give each student a copy of the question sheets.
Students visit each station and fill in their sheets. Allow the students a few minutes
at each station (use the Teachit Timer to set a time and alarm).

• Students could work in groups of up to six. Give the students one or two sheets
each which they fill in using the information sheets. Each member of the group
could test the rest of the group by asking them the questions on their sheet.

• Ask the students to draw graphs to show how rate of reaction changes as
concentration, surface area, temperature are increased.

• The question sheets could be used independently of the information sheets for
more confident groups.

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