Rate of reaction - citric acid and limestone

2. Rates of reaction
 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. Experiment 1 – using a measuring
cylinder.
 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.

4. Measure volume
on a measuring
cylinder

5. Results 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. Measuring rates 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. GRAPH OF RESULTS
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. GRAPH OF RESULTS
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. GRAPH OF RESULTS
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. Calculation
 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. Experiment 2
 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.
Best method

13. Experiment 3
 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.

15. Factors affecting reaction rates
 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. Factors affecting reaction rates
 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. Factors affecting reaction rates
 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. Maxwell Boltzman distribution

19. Temperature effect

20. Temperature effects explained Only molecules with enough activation energy will
react to form the products.

21. Factors affecting reaction rates
 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. Catalyst effect

23. Catalyst effect

24. Collision theory
 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).

25. Links to factors affecting rate of reaction when limestone reacts
with de-scaling acids.
 http://ie.dynapipe.co.uk/how-to-remove-limescale.htm
 http://en.wikipedia.org/wiki/Limescale
 http://www.movia.ro/decalcifiere_eng.html
 http://www.thor.com/view.asp?id=20130408120303AAmFq15
 http://www.newworldencyclopedia.org/entry/acetic_acid
 http://www.newworldencyclopedia.org/entry/Citric_acid
 http://en.wikipedia.org/wiki/Sulfamic_acid
 http://www.lihuasz.com/news/what_is_sulfamic_acif-en.html
 http://www.yangheng.com/zycp08.htm
 http://uk.answers.yahoo.com/question/index?qid=20130414114029AATzCWd
 http://www.howtocleanthings.com/appliances/how-to-clean-coffee-maker.htm
 http://chowhound.chow.com/topics/360882
 http://scottiestech.info/2009/04/22/descaling-appliances-which-acid-is-best/
 http://www.ceragol.com/en/products/premium-descaler/descaling/
 http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Acetic_acid.html
 http://en.wikipedia.org/wiki/Calcium_carbonate
 http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Calcium_carbonate.html