Investigation into what affects the rates of a reaction.

Authors Avatar

Alice Palmer                           Chemistry Coursework                           Mrs Greenwood

Investigation into what affects the rates of a reaction

Background Information

Reactions occur when particles of different elements or compounds collide, and react together.  The particles need a certain amount of energy for the collisions to be effective.  Particles can gain energy by collisions.  Only collisions with enough energy are effective enough to cause a reaction.  The minimum amount of energy needed for a reaction to happen when the particles collide is called the activation energy.  This diagram shows the activation energy of a reaction.  As you can see, the reactants have a certain amount of energy, through collisions they increase the amount of energy.  At the activation energy the reactants start to react, this makes them lose energy as they turn into the products which have even less energy.

For a reaction to happen the particles must overcome this energy barrier.

Several factors can change the amount of energy each particle has, or the amount of energy needed to overcome this barrier.  These factors change the rate of reaction.

Factors which change rate of reaction

Temperature

Increasing the temperature increases the rate of reaction, because particles collide more frequently and with more energy.  As the temperature is increased, the particles present have more energy.  This has two effects:

  1. The particles move around faster and collide more often- this slightly increases the reaction rate.
  2. Because the particles have more energy, any collisions are more likely to result in particles reacting- this has a considerable effect on reaction rate.

An example of temperature affecting reaction rate can be shown in the reaction between sodium thiosulphate and hydrochloric acid- increasing the temperature by just 10 degrees C can double the reaction rate.

Concentration

Increasing the concentration of solutions will increase reaction rate because more particles are present in the same volume, so they are closer together and will collide more often to react.  When the solution is diluted with more water the solute particles are more spread out and so less likely to collide and react.

Pressure

Increasing the pressure of reactions involving gases increases the reaction rate, since the gas particles are closer together and collide more often to react.  This is similar to increasing the concentration of a solution.

Particle Size

The smaller the particle size within the same overall mass, the larger the surface area over which the reaction can occur, and the faster the reaction rate.  This means more collisions take place so the reaction is faster.

Catalysts

Catalysts increase the rate of reaction without themselves being used up or chemically changed.  Catalysts work by lowering the activation energy barrier, this means more reactants can begin to react sooner to turn into the products.  An example of a catalyst is manganese dioxide powder; this speeds up the breakdown of hydrogen peroxide into water and oxygen.

Enzymes

An enzyme is a biological catalyst.  Many of these are found in the human body, for example, saliva, and amylase.

Preliminary Practical Work

I conducted some preliminary practical work to test whether my background research is correct.  I will look at the reaction between Calcium Carbonate and Hydrochloric acid, and see whether the factors that I have researched do actually affect reaction rate.  I will test temperature, particle size and concentration.  I am looking at the amount of fizzing produced when calcium carbonate and hydrochloric acid react to become calcium chloride, carbon dioxide and water.

Join now!

Calcium carbonate + hydrochloric acid         Calcium chloride + carbon dioxide + water

CaCO3 + 2HCl             CaCl2 + CO2 + H2O

The amount of fizzing does not need to be measured very accurately because these preliminary experiments are qualitative experiments, not quantitative, just to show that the factors which I have researched do actually have some affect on reaction rate in the way in which I expect them to.  I will just record which sample from each experiment is the fastest and which is the slowest from observation, times or other detailed results are ...

This is a preview of the whole essay