The rate and extent of chemical change - Paper 2

Rate of Reaction

The change in concentration of a reactant or product over time. It can be calculated as:

• \text{Rate} = \frac{\text{Quantity of reactant used}}{\text{Time}}
• \text{Rate} = \frac{\text{Quantity of product formed}}{\text{Time}}. Common units include g/s, cm^3/s, or mol/s.

Collision Theory

States that for a reaction to occur, particles must collide with sufficient energy (the activation energy) and the correct orientation.

Activation Energy (E_a)

The minimum amount of energy required for a chemical reaction to occur upon collision.

Factors Affecting Rate

The rate of chemical change is influenced by:

• Temperature
• Concentration (for solutions)
• Pressure (for gases)
• Surface Area (for solids)
• Catalysts

Effect of Temperature

Increasing temperature increases the kinetic energy of particles, leading to more frequent collisions and a larger proportion of collisions having energy higher than the activation energy (E_a).

Effect of Concentration and Pressure

Higher concentration or pressure increases the number of particles in a given volume, which increases the frequency of collisions between reactant particles.

Effect of Surface Area

Increasing the surface area (by breaking solids into smaller pieces) increases the surface area to volume ratio, exposing more particles to collisions and increasing the reaction rate.

Catalyst

A substance that increases the rate of reaction by providing an alternative reaction pathway with a lower activation energy (E_a). The catalyst is not consumed in the reaction.

Reversible Reaction

A chemical reaction where the products can react to reform the original reactants, represented by the symbol \rightleftharpoons. Example: A + B \rightleftharpoons C + D.

Dynamic Equilibrium

A state in a closed system where the forward and reverse reactions occur at the same rate, resulting in no overall change in the concentrations of reactants and products.

Le Chatelier's Principle

If a change is made to the conditions of a system at equilibrium, the system will shift its position to counteract the change (e.g., changes in temperature, concentration, or pressure).