2. Chemical reactions take place at very
different rates – some are very fast (like
explosions) and others may take months or
years to proceed.
In a chemical reaction which produces a gas
the rate can be measured by determining the
volume of gas produced as time passes.
Limestone produces carbon dioxide gas when
it reacts with an acid. The rate of production
of carbon dioxide can be measured in several
ways.
3. In this experiment the reagents are calcium
carbonate (limestone) and citric acid.
The products are calcium citrate, carbon
dioxide gas and water.
The rate of the reaction is measured by
measuring how fast the carbon dioxide gas is
produced.
The limiting reagent is the amount of citric
acid. This is the first reagent to be use up.
5. Rate of reaction experiment
Time (s) Volume of Carbon Dioxide (ml)
0 0
30 16
60 25
90 31
120 34
150 35
180 36
210 36
240 36
6. We can record the rate using this relation|:
Rate of reaction = change in recorded property
time for the change
Actual rate is the gradient of the line of the
product concentration versus time graph.
Average rate is the gradient of the line joining
the two point in time over which the rate is
being measured.
7. 0
5
10
15
20
25
30
35
40
0 50 100 150 200 250 300
Volumeofhyrdoger
Time (s)
Rate of reaction experiment.
Rapid
reaction here
Reaction slows
down here.
Reaction
stops here
8. 0
5
10
15
20
25
30
35
40
0 50 100 150 200 250 300
Volumeofcarbondioxide
Time (s)
Rate of reaction experiment.
Rate of reaction experiment Volume
of Hydrogen (ml)
Rate at the start of
the reaction.
9. 0
5
10
15
20
25
30
35
40
0 50 100 150 200 250 300
Volumeofcarbondioxide
Time (s)
Rate of reaction experiment.
Rate of reaction experiment Volume
of Hydrogen (ml)
Average rate of
reaction between
0s and 200s.
10. Calculate the number of moles of carbon
dioxide produce in experiment 1 above.
Volume of carbon dioxide = 36ml
1 mole of carbon dioxide = 24000 ml
Number of moles of carbon dioxide
= 36 ÷ 24000
= 0.0015 moles
11. In this experiment calcium carbonate reacts
with ethanioc acid (acetic acid).
The rate of reaction is measured by collecting
the carbon dioxide gas produced in a gas
syringe.
The results can be processed in the same way
as those for experiment 1.
12.
13. In this experiment calcium carbonate reacts
with citric acid.
The rate of reaction is measured the mass of
the remaining chemicals.
The loss in mass is due to the escaping
carbon dioxide gas.
The results can be processed in the same way
as those for experiment 1 except that the
factor changing is the mass and not the
volume.
14.
15. Concentration
The higher the level of concentration (or
pressure in gases) the faster the reaction.
This is due to increased collisions between
reacting particles.
16. Surface area in solids
The larger the surface area of a solid the
faster the reaction. Finely divided substances
have much larger surface areas than large
chunks of a solid.
This is due to increased collisions between
reacting particles.
17. Temperature
The higher the temperature the faster the
reaction.
This is due to increased and more energetic
collisions between reacting particles.
A 10oC rise in temperature often results in a
doubling of the reaction rate.
18.
19.
20. Only molecules with enough activation energy
will react to form the products.
21. Catalysts
Catalysts increase the rates of chemical
reactions.
This is due a lowering of the activation
energy for the reaction.
Catalysts are not consumed in the reaction so
in theory they can be used over and over
again. In practice they are often contaminated
and/or some is lost in a process.
22.
23.
24. Scientists assume all gases are made of particles
in constant random motion. They have regular
elastic collisions with other molecules.
Gas molecules collide with the walls of their
container and exert pressure but do not lose
energy in their collisions and do not attract other
molecules.
The volume of actual gas molecules in a
container is negligible and their average kinetic
energy is proportional to the temperate (Kelvin).