How Does Concentration Affect the Rate of Reaction?

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How Does Concentration Affect the Rate of Reaction?

By Danielle Clarke

Introduction

This investigation is about finding out how concentration affects the rate of reaction in an experiment. Th rate of reaction is the rate of loss of a reactant or the rate of formation of a product during a chemical reaction. I already know that by changing the variables you can alter the rate of reaction by increase or decrease. The variables are:

Temperature:

In terms of particles, if you increase the temperature of a chemical reaction the particles gain kinetic energy and heating then makes them move faster. When particles move faster they collide more often and with more energy, resulting in more successful collisions. A decrease in temperature would have the opposite effect.

Concentration:

An increase in the concentration of a chemical substance reacting with another would result in the particles crowding closer together due to more particles being added. This process makes it easier for the particles to collide more frequently and efficiently, so it speeds up the reaction. Again, a decrease in concentration would have the opposite effect.

Surface Area:

The particles inside a solid cannot be exposed until the outside particles have reacted. However, if the solid is broken down into smaller pieces, more particles are exposed due to an increase in surface area. More particles available to react means more successful collisions will occur, resulting in a faster rate of reaction.

Pressure:

If the pressure is increased the particles in the gas are pushed closer together. This increases the concentration and thus the rate of reaction.

Using Catalysts:

Catalysts speed up (or slow down) reactions. They provide a surface for the particles to meet and react with each other. This increases the rate of reaction by saving time. Particles reacting on these surfaces need less energy to react successfully.

I have chosen to work with the factor concentration. This is because it will be the most practical experiment to be carried out in a classroom. It would take longer to prepare a solid in powdered and unpowdered form, and it is too difficult to get accurate readings due to the inevitabilities of human errors. As gas is mostly colorless it is difficult to gauge a reaction changing the pressure and if a substance is added to give the gas colour, it may influence the outcome of the experiment. Similarly, use of a catalyst complicates things and if used incorrectly could alter the outcome.

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My aim is to see the effects of a change in concentration on the rate of reaction. The reaction I will use is:

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In this experiment I will vary the concentration of Sodium Thiosulphate while keeping everything else constant. As our sources are limited I am going to mix up my own concentrations of Sodium Thiosulphate by diluting the 1.0M available with water. The table below shows how much water is needed to make 50cm3 of Sodium Thiosulphate in the following concentrations:

I predict that as the concentration of the Sodium Thiosulphate increases the rate ...

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