How does concentration affect the rate of a chemical reaction?

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How does concentration affect the rate of a chemical reaction?

By Tom Pattle


Contents

Planning – Pg 2-7

Introduction – Pg 2

Background Knowledge – Pg 2-7

References – Pg 7

Prediction – Pg 8-10

Method – Pg 9

Apparatus – Pg 9-10

Fair test – Pg 10

Analysing evidence –Pg 11-12

Line graphs

Conclusion – Pg 13

Evaluation – Pg 14-15

 

                         


Plan

Introduction

The experiment is about the concentration of sodium thiosulphate affecting the rate of a chemical reaction when using hydrochloric acid. Here is the word equation for the chemicals that will be used:

Sodium thiosulphate + hydrochloric        sodium + water + sulphur + sulphur

                                acid             chloride                dioxide

Also, the symbol equation:

Na2S2O3(aq) + 2HCl(aq)       2NaCl(aq) + H20(l) + SO2(g) + S(s)

When this reaction takes place, a precipitate of insoluble sulphur will form. The time it takes for a cross to be blocked from view will be measured showing the cloudiness of the precipitate and the rate of reaction.

Background knowledge

        For the reaction in this practical to take place, a thiosulphate (S2O32-) ion has to collide with a hydrogen ion (H+). Here is the symbol equation for this chemical reaction that will happen during the experiment:

S2O32-(aq) + H+(aq)       H2O(u) + SO2(g) + S(g)

        But for the reaction to happen, the S2O32- ions and the H+ ions have to collide at the right angle and with enough speed to overcome the activation energy (the activation energy for a reaction is the minimum energy a collision must possess in order to break bonds in the reactant particles) for an effective collision to take place. See diagram:


                        

A collision that results in a reaction is known as an effective collision. But for an effective collision to happen, the collisions have to have enough energy to cause the bonds in the thiosulphate ions to break, so this means not all collisions between thiosulphate and the hydrogen ions produce a reaction. So the relationship between the number of effective collisions and the rate of reaction is that the more effective collisions per second, the faster the rate of reaction. The diagram explains this:

        Previously, an experiment has been carried out in which marble chips and dilute acid was used instead of thiosulphate and hydrochloric acid. This experiment can be used to show how concentration affects the rate of reaction. The experiment shows that if the solution is made more concentrated it means there are more particles of reactant moving between the hydrogen molecules, which makes collisions between the important particles more likely. So increasing the concentration increases the rate of reaction.

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        Also, a trial experiment was carried out using sodium thiosulphate and HCl and it was proven that the temperature affected the rate of reaction.  This trial also helped plan the method used for this investigation. It showed that as the temperature was increased, the time for a cross to disappear was shortened. This means when the temperature is increased the particles all move quicker. So, if they’re moving faster, they are going to have more speed to overcome the activation energy so they can have more collisions. This graph shows this:

There are some other factors that ...

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