Investigation to find out how particle size affects the reaction rate.

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Investigation to find out how particle size affects the reaction rate

Aim: To find out whether particle size affects the rate of a reaction.

The rate of reaction is the speed of the reaction. There are two ways in which the rate of reaction can be measured:

  • Measure how quickly one of the products in the reaction is made
  • Measure how quickly one of the products in the reaction disappears

Collision theory: The theory that we use to explain how different variables change the rate of reaction is called the collision theory. For a reaction to take place, the particles of the substance that are reacting have to collide. If they collide with enough energy then they react. The minimum amount of kinetic energy that two particles need if they are going to react is called the activation energy. There are therefore two main ways of increasing the rate of reaction:

  • Increase the number of collisions
  • Increase the amount of movement (kinetic) energy so that more collisions lead to a reaction.

The four main variables that can change the rate of reaction are:

  • The concentration of the substances reacting
  • The temperature
  • The size of the particles
  • A catalyst being present

Prediction: I believe that if a solid reactant or a solid catalyst is broken down into smaller pieces the rate of reaction increases. The speed increase happens because smaller pieces of the same mass of solid have a greater surface area compared to larger pieces of the solid. Therefore, there is more chance that a reactant particle will hit the solid surface and react. Below is a picture showing this:

The larger molecules can only collide with a few particles, compared to the smaller molecules which can collide with many particles.  This picture proves that reducing the size of particles increases the rate of a reaction because it increases the surface area available for collisions to take place. This increases the number of collisions. However, I think that particle size has no effect on the energy of the particle.

Apparatus:

  • Delivery tube bung – Used to stop gas from going anywhere apart from into the gas syringe.
  • Gas syringe – Used to measure how fast a gas is produced. As the gas is formed it forces the barrel of the syringe back against atmospheric pressure. This gives the volume of gas for that particular pressure.
  • Conical flask – Used to hold all the chemicals ready for the chemical reaction to take place.
  • A stop watch – Used to calculate how much gas is given off every 5 seconds during the experiment.
  • Hydrochloric acid – Used to displace the different particle sizes of calcium carbonate.
  • Calcium carbonate – Used to react with the hydrochloric acid to see whether particle size affects the rate of reaction.
  • Weighing scales – Used to check that the mass of the calcium carbonate remains constant so that it is a fair test.
  • Measuring cylinder – Used to check that the same quantity of hydrochloric acid is used each time.
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I predict that for each of my experiments carried out that the graph will look something like this. I think that the smaller the particle size the quicker the reaction will happen and therefore the higher the line will rise in a shorter time span. To be able to compare my results and test my theory I will but all of the averages for powder, small, medium, large, and extra large, all on one graph so that I can clearly analyse the correlation. ...

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