Factors Affecting Rates of Reaction

Several factors can influence how fast a chemical reaction occurs. These include concentration, particle size, temperature, catalysts, and the nature of the reactants.

Nature of Reactants

The nature of the reactants affects how quickly they react:

• Ionic reactions: Tend to be fast because ions can react as soon as they collide (e.g., the precipitation of silver chloride, $Ag^+ + Cl^- \rightarrow AgCl$
• Covalent reactions: Tend to be slower because bonds must first be broken before new ones can form (e.g., the combustion of methane).

Particle Size

The smaller the particle size, the faster the reaction. This is because smaller particles provide a larger surface area for the reaction to occur.

Demonstration:

• Marble and Hydrochloric Acid: Large lumps of marble (calcium carbonate) react more slowly with hydrochloric acid than powdered marble because the powder has a larger surface area.

Dust Explosions:

• In grain silos, flour mills, and coal mines, fine dust particles can cause violent explosions if ignited, as they have a very large surface area, which increases the rate of combustion.

Concentration of Reactants

Increasing the concentration of reactants increases the rate of reaction. This is because more reactant particles are present, leading to more frequent and effective collisions.

Temperature

Higher temperature increases the rate of reaction.

When the temperature rises:

• Kinetic energy of molecules increases.
• Molecules move faster and more particles have enough energy to overcome the activation energy barrier, leading to more effective collisions. Rule of Thumb: An increase of 10°C usually doubles the reaction rate.