Rates of reaction - citric acid on limestone (calcium carbonate)

Rates of reactionChemical 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.

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.

Measure volume on a measuring cylinder

Results Rate of reaction experimentTime (s) Volume of Carbon Dioxide (ml)

0 030 1660 2590 31

120 34150 35180 36210 36240 36

Measuring ratesWe can record the rate using this relation|:Rate of reaction = change in recorded property time for the changeActual 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.

GRAPH OF RESULTS

0 50 100 150 200 250 3000

5

10

15

20

25

30

35

40

Rate of reaction experiment.

Rate of reaction experiment Volume of Hydrogen (ml)

Time (s)

Vo

lum

e o

f h

yrd

og

er

Rapid reaction here

Reaction slows down here.

Reaction stops here

GRAPH OF RESULTS

0 50 100 150 200 250 3000

5

10

15

20

25

30

35

40

Rate of reaction experiment.

Rate of reaction experiment Volume of Hydrogen (ml)

Time (s)

Vo

lum

e o

f carb

on

dio

xid

e

Rate at the start of the reaction.

GRAPH OF RESULTS

0 50 100 150 200 250 3000

5

10

15

20

25

30

35

40

Rate of reaction experiment.

Rate of reaction experiment Volume of Hydrogen (ml)

Time (s)

Vo

lum

e o

f carb

on

dio

xid

e

Average rate of reaction between

0s and 200s.

CalculationCalculate the number of moles of carbon

dioxide produce in experiment 1 above.Volume of carbon dioxide = 36ml1 mole of carbon dioxide = 24000 mlNumber of moles of carbon dioxide = 36 ÷ 24000 = 0.0015 moles

Experiment 2In 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

Experiment 3In 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.

Factors affecting reaction ratesConcentrationThe higher the level of concentration (or

pressure in gases) the faster the reaction.This is due to increased collisions between

reacting particles.

Factors affecting reaction ratesSurface area in solidsThe 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.

Factors affecting reaction ratesTemperatureThe 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.

Maxwell Boltzman distribution

Temperature effect

Temperature effects explainedOnly molecules with enough activation energy will react to form the products.

Factors affecting reaction ratesCatalystsCatalysts 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.

Catalyst effect

Catalyst effect

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).

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