Rate of Reactions

Definition

A rate of reaction is defined as how fast or slow a reaction occurs. It is measured by the change in quantity of a substance, known as a reactant or product, over a specific period of time.
The units of rate of reaction are usually mol/dm³/s (moles per cubic decimetre per second).

Factors that affect the Rate of Reaction

Temperature: As temperature increases, so does the rate of reaction. This is because the particles have more energy and therefore collide more frequently and with more force.
Surface area: Increasing the surface area of a reactant can increase the rate of reaction as it provides more exposure for collisions.
Concentration: As concentration of reactants increases, the rate of reaction increases. There are more particles in the same volume so collisions are more likely.
Pressure: Increasing the pressure on gaseous reactants increases the rate of reaction. Pressure increases result in particles being closer together and more likely to collide.
Catalysts: Catalysts increase the rate of reaction by providing an alternative reaction pathway with a lower energy requirement. A catalyst is not used up in a reaction.

Collision Theory

For a reaction to occur particles need to collide with each other and they must collide with enough energy. This minimum energy needed for effective collision is known as activation energy.
The rate of reaction is determined by the frequency of effective collisions.
Collision theory states that the faster the particles are moving, the greater the kinetic energy. If the particles have more energy, there is a greater chance of overcoming the energy barrier and causing a chemical reaction.

Measuring the Rate of Reaction

The rate of a chemical reaction can be measured by tracking the loss of a reactant or the production of a product.
The time taken for a reaction to finish can be measured, for instance in the reaction of marble chips with hydrochloric acid, the time taken for all the marble chips to disappear can be tracked.
Plot the amount of reactant remaining or product produced against time on a graph to track the rate of reaction.

Rate Equations and Order of Reaction

A rate equation shows the relationship between the rate of reaction and the concentration of each reactant.
The order of reaction measures how much the rate of reaction changes when the concentration of a reactant is changed. It can be 0, 1 or 2.
Zero order: The rate of reaction doesn’t change with increasing concentration of a reactant.
First order: The rate of reaction is directly proportional to the concentration of a reactant.
Second order: The rate of the reaction is proportional to the square of the concentration of a reactant.

Reversible Reactions

Reversible reactions are those in which the products of the reaction can themselves react to produce the original reactants.
Le Chatelier’s Principle states that a change in temperature, pressure, or concentration of a reactant can shift the direction of a reversible reaction to counteract that change.

Remember that understanding these topics requires consistent practice, application of principles in different scenarios and regular monitoring of your comprehension.