Chemical Reactions - Rate of reaction (Concentration, Temperature, Surface area, Catalysts)

The rate of reaction is the change in concentration of a reactant or product per unit time. It is commonly expressed in units such as $\text{mol dm}^{-3}\text{s}^{-1}$ or $\text{g/s}$.

Collision Theory states that for a reaction to occur, reactant particles must collide with each other with a minimum amount of energy called the activation energy ($E_a$) and in the correct orientation.

Increasing the concentration of a solution or the pressure of a gas increases the number of particles per unit volume. This leads to a higher frequency of effective collisions, thus increasing the reaction rate.

Raising the temperature increases the average kinetic energy of the particles. This leads to a higher frequency of collisions and, crucially, a much larger fraction of particles possessing energy $\ge E_a$.

For solid reactants, increasing the surface area (by grinding the solid into a powder) exposes more particles to the other reactant, increasing the frequency of collisions at the surface.

A catalyst is a substance that increases the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy ($E_a$). The catalyst itself remains chemically unchanged at the end of the reaction.

The rate of reaction can be measured by monitoring the volume of gas produced ($V$), the decrease in mass of the reaction mixture ($m$), or the time taken for a color change/precipitate to form.