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An Investigation into the Factors which Influence the Rate of a Chemical Reaction.

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Introduction

An Investigation into the Factors which Influence the Rate of a Chemical Reaction Aim The aim of this experiment is to find out what affects the rate at which a reaction occurs between sodium thiosulphate and hydrochloric acid. I want to find out whether and to what degree varying the concentration of sodium thiosulphate has any effect on the rate of reaction. Prediction I predict that the greater the concentration of Sodium Thiosulphate solution the faster the chemical reaction will take place. I think the concentration of a solution affects the rate of reaction because: 'The rate of reaction depends on how frequently the molecules of the reacting substances collide. A more concentrated substance has more molecules with a set volume than one which is more dilute one. This means because there are more molecules about, the frequency of collisions is greater and the reactions happen faster.' Method To find out what effect the concentration has on the rate of reaction, I will be measuring the time it takes for the reaction to complete when various different concentrations of sodium thiosulphate are used. ...read more.

Middle

-Size of Conical Flask This doesn't affect the rate of reaction, because it isn't included in the reaction itself. But it does affect our measurement of how long the reaction has taken to complete. If the conical flask is wider then the cloudiness will appear less concentrated because it will be spread across the larger area of the bottom of the conical flask, this will lead to it taking a longer time for the cross to disappear. -The Cross The cross could affect the results depending on how easily it can be seen. If it was very light, the measurement of how long the reaction took to make it disappear completely would be less, so this would mean the rate of reaction would seem faster. I can keep this constant by using the same laminated cross each time. -Movement of Reacting Mixture If the conical flask is shaken during the reaction then it may speed up making the rate of reaction quicker. Also if the mixture was to be stirred it would force the particles to collide more than they would have. As I have no way of keeping the stirring constant I will prevent any change from happening by not moving the mixture in any way. ...read more.

Conclusion

This makes collisions between the particles more likely. In a liquid increasing the concentration means having the reacting substance less dilute. The more water added means there are fewer molecules to react with as some have been replaced with that of water molecules. This is the factor I intend to change in my experiment. This should be easier to control than other methods of controlling reactions. Heat * The reason reactions happen slowly is because of an energy threshold below which a reaction will not take place. A certain amount of energy is required before the reaction will begin, this is called activation energy. This varies between different chemical reactions. A common way of speeding up reactions is to use heat, initially this makes the particles move quicker, giving them more kinetic energy, so more of them overcome the activation threshold, increasing the rate of reaction. Catalyst * Basically a catalyst is a substance which increases the speed of a reaction without being changed or used up in the reaction. Catalysts work by providing an alternative route for the reaction that has lower activation energy than that of the uncatalysed reaction. Because the activation energy along the catalysed route is smaller, more of the colliding molecules have the minimum energy needed to react, and so the rate of reaction is increased. ...read more.

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