GCSE Chemistry

GCSE Chemistry – Uzma Tariq

TO INVESTIGATE THE RATE OF THE REACTION BETWEEN DILUTE HYDROCHLORIC ACID & SODIUM THIOSULPHATE

A. Introduction

In order to investigate the rate of reaction between a dilute solution of hydrochloric acid and a solution of sodium thiosulphate, the variables that can affect the rate of reaction between any two reactants must, firstly, be identified. These variables are discussed below using the particle theory of matter, which is; that all matter is composed of particles and their behaviour can be predicted. The particles in this chemical reaction are the atoms and molecules of the reactants and the products of the reaction. Under normal conditions the particles are vibrating about a mean position, the level of energy processed by the particles can be increased by making them vibrate more. Collision theory says that reactions will proceed faster when the collisions are more frequent and with sufficient energy. The following variables affect rates of reaction.

Concentration of the reactant(s).

A higher concentration will result in a faster rate of reaction and vice versa. This can be explained by the ‘particle theory’; a high concentration of reactants will mean there are more particles of the reactants involved in the reaction. This, in turn, will increase the rate of reaction by creating more collisions between the particles, and so creating a higher chance of more successful collisions.

Pressure of the container in which the reactants are placed. (Gas only)

Increasing the pressure can be explained in the same way as increasing concentration, because increasing the pressure of a mixture of gasses forces the particles closer together and so increases the concentration. If the particles are closer together there will be more collisions and therefore more successful collisions.

Temperature of reactants.

Increasing the temperature speeds up the movement of the particles and increases the rate of reaction. Heating a chemical transfer’s kinetic energy to the chemical’s particles. More kinetic energy means that the particles move faster. As they are moving faster there will also be more collisions per second. The particles also have more kinetic energy, so more collisions will lead to a reaction because these collisions have more energy, which leads to more successful collisions.

Light

Using sunlight or UV light has the same effect as increasing temperature. Some chemical reactions take place faster when they absorb light. For example the formation of silver from silver salts takes place when photographic film is exposed to light. In sunlight, green plants are able to carry on the process of photosynthesis.

Surface area (Solid Only)

When one of the reactants is a solid, the reaction must take place on the surface of the solid. By breaking the solid into smaller pieces, the surface area is increased, giving a greater area for collisions to take place and so causing an increase in the rate of reaction.

Using a catalyst

A catalyst is a substance that alters the rate of reaction but remains chemically unchanged and is not used up at the end of the reaction. A catalyst speeds up the reaction. Using a catalyst lowers the activation energy for the reaction. More collisions have sufficient energy for reactions to occur.