Rates of Reaction

Basics of Reaction Rates

Reaction rate describes how quickly or slowly a reaction takes place.
This is often quantified as the speed at which reactants are used up or products are formed.
The speed of different reactions can vary from extremely fast (like explosions) to ones that take years (like rusting).

Factors Influencing Reaction Rates

The concentration of the reactants: High concentration usually increases the reaction rate because it leads to more frequent collisions between particles.
The temperature: High temperature increases the reaction rate because particles move faster and collide more often, and more of these collisions have enough energy to result in reaction.
The surface area exposed to other reactants: Large surface area increases the reaction rate because it allows for more collisions to happen concurrently.
The presence of a catalyst: Catalysts can significantly increase the reaction rate by lowering the activation energy of the reaction.

Collision Theory

The collision theory explains how chemical reactions occur and why rates of reaction alter.
For a reaction to occur, particles must collide with each other, and this collision must have sufficient energy, called the activation energy.
Only a fraction of the total collisions cause chemical change; these are called successful collisions.

Measuring Rates of Reaction

Reaction rates can be determined by observing changes in physical properties, including colour, precipitate formation, gas production, or changes in mass.
The change in concentration of reactants or products over time may also be measured.

Rate Equations

The specific rate of a reaction can often be expressed by a rate equation, which includes the rate constant, the concentrations of the reactants, and their respective order of reaction.
The order of reaction describes the effect of changing the concentration of one of the reactants on the overall rate of reaction.

Catalysts and Reaction Rates

A catalyst accelerates a reaction by providing an alternative pathway for the reaction that has a lower activation energy.
Catalysts are not consumed in the reaction, hence can be used repeatedly.
Biological catalysts are called enzymes, and they play a crucial role in many biological processes.