Rates of Reaction - The concentration of hydrochloric acid and the rate of reaction with sodium theosulphate

Rates of Reaction - The concentration of hydrochloric acid and the rate of reaction with sodium theosulphate

Introduction

During a chemical reaction, particles collide with each other. This collision causes certain bonds to break and new ones to be formed. A certain amount of energy is needed to allow a reaction to take place.

This is called the activation energy; it’s the minimum quantity of energy that is required. There are certain factors that can affect the rate of reaction. These are surface area, temperature, concentration and catalysts.

The surface area is a very big factor in the rate of reaction.

Reactions only occur on the surface, because this is where the collisions will occur. If a solid is broken into smaller pieces, the surface area is increased. This leaves more area where the reaction can take place, thus increasing the rate. If the reactant is in the form of one large solid, the reaction will take longer, therefore decreasing the rate.

The temperature is also a major factor. When the temperature increases, the particles consequently heat up. This causes the kinetic energy in them to increase, therefore they move around faster. This means that the rate in which they collide with one another will increase. By increasing the concentration of something, more particles are introduced in the same volume. This would mean that the likelihood of collisions will increase. This would increase the rate of reaction. On the opposite angle, the lower the concentration, the less chance of collisions. Therefore the rate of reaction will decrease.

Catalysts can be found in the form of transition metals. These speed up the rate of reaction. However, the catalysts themselves are not used up.

Aim

Our aim is to see how the change in concentration of hydrochloric acid might affect the rate at which it reacts with sodium theosulphate.

Prediction

When sodium theosulphate and hydrochloric acid react together, many products are created.

Na2 S2 O3 (aq) + 2HCl (aq) à 2NaCl (aq) +H2O (l) + SO2 (aq) +S (s)

The equation above shows all the products of the reaction between hydrochloric acid and sodium theosulphate. The products are sodium chloride (aqueous solution), water (liquid), sulphur dioxide (aqueous solution) and sulphur (solid).

The sulphur, being a solid, turns to liquid cloudy and opaque. A certain amount of sodium is needed to turn the solution cloudy enough to be opaque.

Increasing the concentration of a liquid increases the amount of particles; therefore there will be more successful collisions. Because of this, more sulphur will be produced.

Overall, the higher the concentration, the more sulphur will be produced. Therefore, the liquid will become opaque quicker.

I predict that my graph will look like this (below) when I plot the