An Experiment To Investigate The Relationship Between The Surface Area And Rate Of Reaction

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GCSE Coursework:SC1 Investigation

An Experiment To Investigate The Relationship Between The Surface Area And Rate Of Reaction

Introduction

The rate of reaction (reaction velocity) may be defined as the rate of change of concentration of a stated reactant or product. The rate of a reaction is found by measuring the amount of a reactant used up per unit of time or the amount of a product produced per unit of time. A reaction can be made to go faster or slower by changing a number of factors. In order for a reaction to occur certain things are necessary: particles must collide with each other and the collision must have enough energy for the reaction to occur. If this happens the original bonds are broken and new bonds are formed – so that new products are formed. Successful collisions (those with sufficient energy) can be increased (or decreased) by a number of factors.

These key variables consist of temperature, concentration, surface area and use of and type of a catalyst.  To examine the relationship between the rate of reaction and surface area I must choose to vary only surface area keeping the other variables constant.

Surface area of solid – The surface area has an effect on the rate of reaction. If the solid has a large surface area per unit mass then there are more opportunities for collisions to occur between the solid and liquid. This is because there is more chance for collisions to occur. If the surface area per unit mass is small, collision can only occur with the outer atoms and is therefore limited. The diagram below illustrates this:

This relationship is proportional i.e. as one doubles so does the other.

The temperature of the reaction - When the temperature is low, the particles in the reaction do not have much energy and move slowly so collision is less likely to occur. However on heating, particles take in energy causing them to move faster and collide more often. Also when a collision occurs they have more energy and so are more likely to be successful in breaking and reforming bonds than when they have less energy and are moving more slowly. Therefore the rate of the reaction will increase. As a rule of thumb when the temperature increases by 10C, the rate of the reaction roughly doubles.

 The concentration of the acid - The more concentrated the solution, the more particles of reactant are present in a given volume and the greater the chance of a collision occurring. In dilute acids, with fewer particles the chance of collisions occurring is reduced. Therefore if concentration is increased, the reaction rate also increases. This also applies in reactions between two gases when increasing the pressure has the same effect as increasing the concentration.

The presence of a catalyst - A catalyst increases the rate of a chemical reaction without itself being used up. Catalysts are usually transition metals. In the presence of a catalyst, less energy is needed by a collision in order to be successful. Therefore there are relatively more successful collisions and so the reaction rate increases.

I have decided to investigate how a change in surface area will affect the rate of the reaction between calcium carbonate (marble chips) and hydrochloric acid. The word equation for this reaction is:

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

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                CaCO3(s) + 2HCL(aq) = CO2(G) + H2O(l) + CACL2(aq)

I have decided to vary this factor because it is fairly easy to control; the other variables are less suitable for this experiment.  Temperature is a very difficult variable to use in this experiment. I would have problems collecting accurate results because of the difficulty of keeping the heat source constant during the reaction. I also chose not to vary the concentration of hydrochloric acid because the highest concentration available for my use was 4M and I felt I could not achieve the desired variation with such limited concentrations.  I ...

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