The purpose of this investigation is to find out the different factors which, affects the rate of a reaction. Then I will further investigate into one factor which will be temperate, I will observe how temperature will affect the rate of a reaction.

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Saima Ahmad          

September 2005

An Investigation to find out what factors affect the rate of a reaction

The purpose of this investigation is to find out the different factors which, affects the rate of a reaction. Then I will further investigate into one factor which will be temperate, I will observe how temperature will affect the rate of a reaction.

Na2 S2O3 (aq) + 2HCl (aq)  2NaCl (s) + S (s) + SO2 (g) + H2O (aq)

A ‘rate of a reaction’ tell us how quickly a chemical reaction takes place. To work out the rate of a reaction I will have to actually conduct an experiment. During any reaction we can measure two things, how much reactant is used up in a certain time ore how much product is formed in a certain time.

In a chemical reaction, there are substances, these substances are made from particles, and they can be ions, atoms, or molecules. In order for a chemical reaction to occur particles must collide to create head on collisions. Therefore, there particles must collide with enough energy to make them collide faster and harder. This energy is needed so the existing bonds breakdown and create new bonds, this is called the collision theory. This is the basic theory which occurs in the chemical reaction.

There are five factors that affect and can alter the rate of a reaction they are:

  • Surface area
  • Catalyst
  • Pressure
  • Temperature
  • Concentration

Surface Area

In a reaction the surface area affects a chemical reaction, if one of the reactants is a solid; the surface area will affect how fast a reaction takes place. This is because they two types of molecules can only collide into each other if they are in liquid solid interface, on the surface of the solid. Therefore the longer the surface area, the faster the reaction will be. In other words the smaller the particles the bigger the surface area they have. The size of the particle increases collisions.

           

A Catalyst

A catalysts is used to speed up chemical reactions only a very small amount of catalysts are required to produce a dramatic change in the rate of a reaction. This is really because the reaction proceeds by a different pathway when the catalyst is present. By adding extra catalysts will make absolutely no difference. When two different molecules bump into each other they might react to make new chemicals. When ‘collisions’ occur between molecules, it depends upon how frequently the molecules collide to affect the rate of the reaction, the purpose of a catalyst is o increase the chance of molecules colliding.

A catalysts increases collisions

A catalysts works by giving the reacting particles a surprise to stick to where they can bump into each other, this increases the number of collisions.

Pressures

In reactions between gases, increasing the pressure increases the rate of a reaction. The molecules in a gas are very spread out, for the two chemicals to react; there must be a lot of collisions. By increasing the pressure, we squeeze the molecules together so this will increase the frequency of collision between them. Therefore this will cause the rate of the reaction to increase.

Temperature

Temperature also affects the rate of a chemical reaction. When the temperature increases, the molecules gain energy and they collide together faster and harder. This energy is needed to break the existing bonds so that the particles are free to make new bonds. The higher the temperature, the higher the average speed increases, so a larger proportion of the collisions transfer sufficient energy for the particles to react. The faster a particle, the more kinetic energy it has and so the more chance it has of reaching the activation energy in a collision.

Concentration

By increasing the concentration of the reactants will increase the frequency of collisions between the two reactants. In a solution of higher concentration, particles are closer together; therefore they have a greater chance of colliding. The more collisions the reaction rate is greater. For example, in a solution of an acid and marble chips and when they collide.

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The acid particles are randomly moving in the water. As you increase the concentration of the acid, therefore there are more acid particles in the same volume. The frequency of collisions between the two reactants increase, therefore the rate of reaction increases.

The factor I’m going to considered in investigate and observe is how temperature affects the rate of a reaction. I will investigate the changes caused to the solution of hydrochloric acid and sodium thiosulphate when the temperature is increased slightly each time I attempt the experiment.

Changes in ...

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