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Rate of Reaction

The document discusses (1) how reaction rate is measured, (2) collision theory and how effective collisions cause reactions, and (3) factors that affect reaction rate such as surface area, concentration, temperature, and catalysts according to collision theory.

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kaila kilogram
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106 views19 pages

Rate of Reaction

The document discusses (1) how reaction rate is measured, (2) collision theory and how effective collisions cause reactions, and (3) factors that affect reaction rate such as surface area, concentration, temperature, and catalysts according to collision theory.

Uploaded by

kaila kilogram
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Learning Outcomes

• I can explain what ‘reaction rate’ means and how to


measure the rate of reaction
• I can explain how reactions happen due to collisions
between particles
• I can explain how surface area, concentration and
temperature affect the reaction rate using collision
theory
Rate of Reaction
the speed at which a chemical reaction
occurs.

Some reactions
are quick Some are not

The rate of a reaction can be altered


Measuring rate of reaction
Two common ways:
1) Measure how fast the
products are formed
• Colour change
• Gas formation

2) Measure how fast the


reactants are used up
Rate of reaction graph
Amount of
product Slows down as time passes as
formed reactants are used up

Reaction begins Stops after a certain time – graph levels out as


rapidly one (or both) reactants have been used up.

Time
Collision Theory

“For a reaction between two


particles to occur, the particles
must collide and the collision must
be effective”
Effective Collisions
• When the particles collide with enough kinetic
energy and the correct orientation to break the
bonds between particles so new bonds can form.

Collisions can occur and yet result in no reaction


if there is insufficient energy or incorrect
orientation.
How do reactions occur?
Reactions take place when particles collide with a
certain amount of energy.

Not enough energy –


no reaction
How do reactions occur?
Reactions take place when particles collide with a
certain amount of energy.

Incorrect orientation –
no reaction
How do reactions occur?
Reactions take place when particles collide with a
certain amount of energy.

Enough energy and


correct orientation –
reaction!
Activation Energy
• The minimum amount of energy needed for the
particles to react is called the activation energy, and
is different for each reaction.

• If particles collide with less energy than the


activation energy, they will not react.

Kick-starting Reactions - Activation Energy


Collisions and Rate
• The more frequently effective collisions occur the
faster the rate of reaction.

To change the rate of reaction we can:

• Change the concentration of reactants


• Change the temperature of the reaction
• Change the surface area of reactants
• Using a catalyst
Concentration
• Increasing the concentration of a reactant increases
the number of particles per volume . This increases
the frequency of collisions. Which increases the rate
of the reaction
Surface Area
• Increasing the surface area of a reactant
increases the number of particles available to
react. This increases the frequency of collisions
which increases the rate of the reaction.
Temperature

• Increasing the temperature of a reaction


increases the kinetic energy of the
particles. The particles collide more often
and with more energy this increases the
frequency of effective collisions which
increases the rate of reaction
Catalyst
• What is a catalyst?
• A catalyst is a substance which speeds up a reaction, but is
chemically unchanged at the end of the reaction. When the
reaction has finished, you would have exactly the same
mass of catalyst as you had at the beginning.
• Examples:
Manufacture of ammonia by the Haber Process
Catalyst: iron
Catalyst

• Adding a catalyst has the


effect of shifting the
activation energy
• A catalyst provides an
alternative route for the
reaction
• That alternative route
has a lower activation
energy.
Catalyst
1. The correct form of words is

"A catalyst provides an alternative route for the reaction


with a lower activation energy."

It does not "lower the activation energy of the reaction".


There is a subtle difference between the two statements
that is easily illustrated with a simple analogy.
In Summary
• What does ‘reaction rate’ mean and how to measure
the rate of reaction ?
• How do collisions between particles make reactions
happen ?
• What are the factors that affect the rate of
reactions ?
• What do catalysts do to a reaction ?

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