C7 Chemical reactions
C7 Chemical reactions
C7.1 Rate (speed) of reaction
Core
1 Describe practical methods for investigating the rate of a reaction which produces a gas
2 Interpret data obtained from experiments concerned with rate of reaction
3 Suggest suitable apparatus, given information, for experiments, including collection of gases
and measurement of rates of reaction
4 Describe the effect of concentration, particle size, catalysts and temperature on the rate of reactions
5 Describe and explain the effect of changing concentration in terms of frequency of collisions between
reacting particles
6 Describe and explain the effect of changing temperature in terms of the frequency of collisions between
reacting particles and more colliding particles possessing the minimum energy (activation energy) to react
Note: Candidates should be encouraged to use the term rate rather than speed.
C7.2 Redox
Core
1 Describe oxidation and reduction in chemical reactions in terms of oxygen loss / gain (Oxidation state limited to
its use to name ions, e.g. iron(II), iron(III), copper(II).
2 Define and identify an oxidizing agent as a substance which oxidizes another substance during a redox reaction and a
reducing agent as a substance which reduces another substance during a redox reaction
The rate of a reaction is a measure of how
quickly a reactant is used up, or a product is
formed.
Time
/s
Volume of gas
produced
/ 𝐜𝐦𝟑
Increased in
volume
/ 𝐜𝐦𝟑
0
0
0
30
50
50
60
100
50
90
142
42
120
170
28
150
181
11
180
181
0
210
181
0
Volume /
2 Interpret data obtained from experiments concerned with rate of reaction
180
 Rate of reaction increases from 0s to 60s.
 Rate of reaction decreases after 60s.
 Reaction comes to a stop from 180s onward.
How do you find out the rate of reaction between CaCO₃ and HCl?
Delivery tube
Retort stand
Conical flask
Reactants
Questions to answer
1) What are the reactants used in this experiment?
2) What are the apparatus used?
3) Decide on the independent variables and dependent variables.
4) What are the readings/data to record?
5) What are the precautions to take in order to minimize accidents and
ensure accurate/reliable data
Methods of collecting gas in experiment
Water Displacement
- In a large bowl filled with water, put a measuring cylinder full with water upside down.
- Set up a reaction mixture in a sealed container with a single tube allowing the gas to escape.
- Put the gas tube under the water-filled measuring cylinder
- The gas produced will be collected in the measuring cylinder, displacing the water
downwards.
- Now, the volume of gas produced can be recorded at a constant time interval, e.g.10s
- The volume and time readings are recorded in a table.
Gas Syringe Method
- Set up a reaction mixture in a sealed container with a single tube allowing the gas to escape.
- On the end of the tube, join a gas syringe.
- As the gas is produced, the gas syringe will be pushed backwards.
- The amount of gas produced can also be recorded easily, using the volume markers on the
syringe.
- Amount of gas produced can be recorded in a constant time interval, e.g.10s
- The volume and time readings are recorded in a table.
3 Suggest suitable apparatus, given information, for experiments, including collection of gases
Collecting gas using water displacement method
Apparatus suitable for
experiment on
rate of reaction:
Conical flask,
stop cork,
graduated cylinder,
thistle tube,
delivery tube,
trough,
beehive shelf,
stopwatch.
Apparatus suitable for experiment on rate of reaction:
Conical flask, stop cork, gas syringe, delivery tube, stopwatch.
Collecting gas using a gas syringe
4 factors that affect the rate of a chemical
reaction:
•temperature
•concentration
•particle size
•use of a catalyst
Rate of reaction is increased by increasing the temperature
Time of reaction
Rate of reaction is increased by decreasing the size of particles
Rate of reaction is increased by increasing catalyst
4 Describe the effect of concentration, particle size, catalysts and temperature on the rate of Reactions
 If the concentration of reactants is increased, there are more reactant particles
moving together.
 There will be more collisions and so the reaction rate is increased.
 The higher the concentration of reactants, the faster the rate of a reaction will be.
Particle size (only solids) affect the rate of reaction
 We know that meat can be cooked more quickly by cutting them into smaller
pieces.
A catalyst speeds up the rate of a reaction but it is not used up in the reaction. If a catalyst is present, the reacting
particles can collide more successfully with less energy and so the reaction can take place at a lower temperature.
Temperature
 If the temperature is increased, the particles have more energy and so move quicker.
 Increasing the temperature increases the rate of reaction because the particles collide more often and
with more energy.
 This means more molecules will have the minimum energy (activation energy) to react.
 The higher the temperature, the faster the rate of a reaction will be.
 The graph shows the rate of the reaction between
hydrochloric acid and calcium carbonate.
 Notice how an increase in temperature leads to an increase
in the speed of release of carbon dioxide, but not the
total volume of carbon dioxide released.
How to explain that at higher temperature, the rate of reaction increases?
C7.2 Redox Core 1 Describe oxidation and reduction in chemical reactions in terms of oxygen loss / gain
(Oxidation state limited to its use to name ions, e.g. iron(II), iron(III), copper(II).)
Oxidation is the gain of oxygen by a substance.
It is also the loss of electrons from a
substance.
Eg, magnesium is oxidised when it reacts with
oxygen to form magnesium oxide:
magnesium + oxygen → magnesium oxide
2Mg + O2 → 2MgO
Reduction is the loss of oxygen from a
substance.
It is also the gain of electrons by a substance.
Eg, copper(II) oxide can be reduced to form
copper when it reacts with hydrogen:
copper(II) oxide + hydrogen → copper + water
CuO + H2 → Cu + H2O
Usually, oxidation and reduction take place at the same time in a
reaction. We call this type of reaction a redox reaction
(red – reduction, ox – oxidation).
Remember it with the acronym OILRIG
Oxidation Is Loss , Reduction Is Gain
2 Define and identify an oxidising agent as a substance which oxidises another substance during a redox reaction and a
reducing agent as a substance which reduces another substance during a redox reaction
Oxidising agent and reducing agent
the oxidising agent is the chemical that causes oxidation by providing oxygen
the reducing agent causes the other chemical to be reduced by removing
oxygen
Take a look at the following thermite reaction:
aluminium + iron(III) oxide → iron + aluminium oxide
2Al + Fe2O3 → 2Fe + Al2O3
Aluminium has been oxidised. This means that the iron(III) oxide is the oxidising
agent.
We can also see that the iron(III) oxide has been reduced. This means that the
aluminium is the reducing agent.
Iron combines with oxygen in the presence of water to form
rust or iron oxide which is Fe(III)Oxide
 Which element has
been oxidized?
 Who is the oxygen
provider?
 For reactants Fe and O2 ,
 Which one loses
electrons?
 Which one gains
electrons?
 Which element has
been reduced?
 Which element is the
oxidising agent?
 Which element is the
reducing agent?
Carbon monoxide
 Name the compound that has been oxidized?
 Who is the oxygen provider?
 Name the compound that has been reduced?
 Name the reactant that loses electrons?
 Name the reactant that gains electrons
 Name the oxidising agent?
 Name the reducing agent?
Carbon dioxide
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Assignment / homework
Page 288 questions 1,2,3,4,5
Page 291 questions 1,2,3
Page 295 questions 1,2,3
Page 298/9 questions 1,2,3,4
Page 301 questions 1,2
Page 302 questions 1,2