Essay on The Effect of Concentrations on Rate of Reaction

Submitted By LalaLexi
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Pages: 6

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Measuring the rate of reaction, when dilute sodium thiosulphate solution and dilute hydrochloric acid are mixed.


I predict that the higher the concentration of sodium thiosulphate, the faster the rate of reaction.


In this experiment I intend to test the collision theory. My aim is to see if the concentration of sodium thiosulphate will affect the rate of reaction.


In this experiment I will vary the concentration of sodium thiosulphate to measure the rates of reaction. I will be mixing different concentrations of sodium thiosulphate with hydrochloric acid, the collision theory says the reaction time will alter; this is what I will be testing.

The collision theory tells us that the larger the surface area, the faster the reaction. So the higher the concentration the more atoms there are to react. There are 4 things that affect the rate of reaction, concentration, surface area, catalysts and temperature.
Concentration can affect the rate of reaction by increasing atoms to collide with each other. The more atoms there are to collide, the faster the rate of reaction.

In reactions where gases are involved, if you increase the pressure the particles will move closer together. The smaller the space in the container, collisions are more likely to occur. If the concentration is weaker, this means there are fewer atoms to collide. If an object has a large surface area, the reaction rate will increase as there is more surface area for the atoms to collide. I hypothesis that the more surface area there is the more space there is for the particles to react. Catalysts change the rate of chemical reactions but are not used up in the reaction.

Examples of catalysts are enzymes, clay, and hydrogen peroxide. These all speed up certain chemical reactions. Enzymes are found in the human body, they are there to break down food and make digestion time shorter. Enzymes can also be found in washing powder, to break down food stains on clothes. Temperature can affect the rate of reaction to a great extent because particles vibrate more at higher temperatures.
The more they vibrate the more chance there is that they will collide with another particle, thus causing the rate of reaction to increase.

In a chemical reaction, the reactants collide with each other.


This diagram shows us that the more pressure there is the more likely it is that the particles will collide.

High pressure

Low pressure

More collisions as the particles are closer together

Not many collisions

Marble in dilute hydrochloric acid

This diagram shows us that surface area does have an effect on the rate of reaction.

1 Large marble cube Marble cube split into 6 pieces

In the experiment I carry out, I will change the concentration and see if different concentrations make a difference.

The equation of this experiment is:

Na2 S2 O3 + 2HCl 2NaCl + SO2 + S + H2O

Sodium thiosulphate + hydrochloric acid sodium chloride + sulphur dioxide + sulphur + water

Health and Safety:

Before the experiment is carried out I must have a safe environment, in order to prevent accidents.

* Wear goggles before touching any chemicals or equipment.

* After the experiment wash your hands thoroughly with liquid.

When sodium thiosulphate and hydrochloric acid react, a gas called sulphur dioxide is released. Sulphur dioxide turns into sulphuric acid when it comes in contact with the moisture in your respiratory system.
The sulphuric acid can burn away layers on your throat, which could cause a sore throat.


· Conical flask
· Measuring Cylinder ( 50cm³ and 10cm³)
· Stop Clock
· Solution of Sodium Thiosulphate
· Solution of Hydrochloric Acid
· Water
· Sheet of paper with an ‘X’ marked on it.

Preliminary Work:

When I done my…