Investigate the effects of the concentration of reactants on rate of reaction

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In this experiment I intend to investigate the effects of the concentration

of reactants on rate of reaction.

Planning

In this experiment I intend to investigate the effects of the

concentration of reactants on rate of reaction. Specifically I will

investigate what effect varying the concentration of hydrochloric acid

has when it is reacted with sodium thiosulphate. The details of how a

reaction works on a molecular level are described by the collision

theory.

The collision theory explains the circumstances under which

collisions between the particles of the reactants involved in a

reaction must collide, in order for a reaction to occur. In order to

react, the individual particles of a reactant must not only collide in

the correct orientation (as explained in the diagram below), but must

also collide with sufficient energy. When both of these are achieved,

the collision is strong enough to break any existing bonds and form

new ones. The minimum amount of energy required in a collision for two

particles to react is called the activation energy, and varies

according to the reactants. Thus, not all collisions are successful in

inducing a reaction; those that do succeed are called fruitful

collisions.

The more fruitful collisions there are in a reaction, the higher the

rate of reaction will be. Rate of reaction may be measured by

observing the speed with which a product of the reaction is produced.

Where a gas is produced it can be measured in one of three ways. By

forcing it to pass through a cylinder of water, we can measure the

amount of water it displaces, and therefore its volume. Similarly, we

can measure its volume using a gas syringe fitted to the top of the

container in which the reaction is taking place. Alternatively, we can

measure the weight that the container and its contents lose as the

reaction's product is given off, this being proportional to the volume

of the product itself. In each of these examples, the reaction is

timed until it has completely finished. When the volume of the

products given off is plotted against the time taken in a graph, the

gradient of the line denotes the speed of the reaction.

Mathematically, rate of reaction can be expressed as follows:

Reaction rate = Change in the amount of substance

Time taken

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If the products are not gases though, methods of observation may be

employed to measure rate of reaction. Some products will cause a

substance created in a reaction to become cloudy. The production of

this precipitate could be measured and timed, although in this case

accuracy becomes more difficult as the product remains in the

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