Rates of Chemical Reactions – using reaction of an acid

on limestone (calcium carbonate)

Monday 10 April 2023

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.

Rates of reaction

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.

Experiment 1 – using a measuring cylinder.

Measure volume on a measuring

cylinder

ResultsRate of reaction experimentTime (s) Volume of Carbon Dioxide (ml)

0 030 1660 2590 31

120 34150 35180 36210 36240 36

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.

Measuring rates

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.

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

Calculation

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.

Experiment 2

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.

Experiment 3

Concentration The 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 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.

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.

Factors affecting reaction rates

Maxwell Boltzman distribution

Temperature effect

Only molecules with enough activation energy will react to form the products.

Temperature effects explained

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.

Factors affecting reaction rates

Catalyst effect

Catalyst effect

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).

Collision theory

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

Links to factors affecting rate of reaction when limestone reacts with de-scaling acids.