C2.4 Rates of Reaction

  • Created by: Fiona S
  • Created on: 10-05-15 11:19

Collision Theory

In the reaction below:

Calcium Carbonate + Hydrochloric Acid --> Calcium Oxide + Carbon Dioxide + Water

Particles of Calcium Carbonate and Hydrochloric Acid have to collide with sufficient energy for a reaction to take place. We call this energy the activation energy.

Effect of Surface Area on Reaction Rate
Prediction: As we increase the surface area the reaction rate will increase. This is because the particles have more space to collide so the particles will collide more frequently with in a set time.

  • more particle of reactant exposed
  • leads to more frequent collisions
  • increased reaction rate
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Effect of Concentration

Concentration is a measure of how many particles there are in a set volume. This means two factors affect concentration:

  • How many particles there are
  • The total volume of solution


Concentration is measured in moldm-3 which means moles per dm3

1000cm3 = 1dm3

Quite often we show this as M.

So if our concentration is 1moldm-3 then there is 1 mole in every dm3

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Rate of Reaction

Reaction Rate is  =  a change in something / time

(http://www.smartlearner.mobi/science/VideoPastPapers/ReactionRates/Images/reaction_rates24.jpg) Cotton wool used to stop fizzing escape if reaction fizzes but lets gas through.

Can measure: change in mass (when we make a gas), volume of gas (gas syringe), change in colour (disappearing cross) make a precipitate (solid that won't dissolve).

To increase reaction rate:

  • Use smaller pieces (increases S.A)(more particles exposed)(more frequent collisions)
  • Increase the temperature (more kinetic energy)(move faster) (more frequent collisions with more force)
  • Increase concentration (more particles in set volume)(more frequent collisions)
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Effect of a Catalyst

A catalyst is a substance which speeds up a chemical reaction. At the end of the reaction the catalyst is chemically unchanged.

In any chemical reaction we have to supply energy to get it started. We call this the activation energy. Some reactions give out a lot of energy and we call this exothermic. Some only give out a little. These are endothermic. Endothermic reactions activation energy is greater than energy released. Exothermic reactions has more energy given out than put in.

Catalysts save time, money and it's reusable

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