How does concentration affect the rate of reaction?

Christina Adenaike

Aim: To investigate how different concentrations of hydrochloric aci9d affect the rate of reaction on marble chip, (calcium carbonate).

Background information: Different reactions take place at different rate. The measurement of the change can take place in a single unit of time; it can take seconds, minutes, hours and even days. It can be either fast or slow. Reaction rates are explained by the collision theory. The collision theory is explained by the rate of reaction. This is when reaching particles collide with each other. In order for particles to react, this depends on how often and how hard they collide. There are four main methods that are explained in terms of increasing the number of collisions so that the rate of reaction also increases between the reacting particles. These are: Temperature, concentration, surface area and a catalyst.

Temperature causes particles to collide faster if the temperature is high and slower if the temperature is low. By increasing the temperature, the reactant particles are supplied with a lot of energy, they move faster and this increases the chance of more successful collisions, because the reacting particles have an increase in energy, the particles can collide hard enough to make a reaction happen.

In year 9, I studied the effect of temperature on the rate of reaction. It was an experiment to investigate the reaction between thiosulphate and acid. This reaction showed that there were faster collisions at 300C than there were at 200C. At higher temperatures, ions have more kinetic energy and collide more often and more vigorously, giving them a greater chance of reacting.

The diagram below is showing the effect of temperature on the speed of a reaction

The time needed to complete the The speed of the reaction

Reaction decreases with increasing increases with increasing

Temperature. Temperature.

The energy used by colliding particles is called Activation energy. This is what the initial energy is known as. It is needed to break existing bonds this process is called endothermic. Energy is released when new bonds form, this process is called exothermic.

The diagram below shows an Energy level diagram.

N.B H= means the energy given off in the experiment.

In the exothermic reaction H is –ve. The diagram show an exothermic reaction because the products are at a lower energy than the

reactants. The difference in height represents the energy given. Out in the reaction (per mole). H is –ve in this case. The initial rise in the line represents the energy needed to break the old bonds. This is the activation energy.

In the endothermic reaction H is +ve. The diagram shows an endothermic reaction because the products are at a higher energy than the reactants. H is +ve. The difference in height represents the energy taken in during the reaction.

Concentration (or pressure for gases) affects the rate of reaction because if the solution is made more concentrated, it means there are more particles of reactant knocking about between the important particles more likely. In a gas increasing the pressure means the molecules are more compressed together therefore there will be more collisions.

Increasing the concentration of a reactant simply means there are more particles, which may collide and so react. More collisions means a faster

reaction.

Surface area (size of solid particles), The reaction between a solid and a liquid is speeded up by using smaller particles of the solid reactant. The reason being is that it is the atoms or ions at the surface of the solid that react, and the ratio of the surface area; mass is greater for small particles than for large particles. Using a powder instead of a lump means the

surface area is greater, which means a greater area

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