Kinetic factors: temperature, concentration, catalyst

What speeds up or slows down a reaction

Three main factors influence the rate of a chemical reaction, without altering its nature or final state: temperature, the concentration of the reactants, and the presence of a catalyst.

Temperature

Raising the temperature increases the reaction rate. The molecules move about more quickly, collide more often and with greater energy, which promotes effective collisions. This is why we keep food in the fridge: the cold slows down degradation reactions.

Concentration

The more concentrated the reactants are, the more frequent the collisions between their molecules, and therefore the faster the reaction. This is why a reaction slows down over time: the reactants are consumed, and their concentration decreases.

The catalyst

A catalyst is a substance that increases the rate of a reaction without being consumed: it remains intact at the end. It works by opening up an alternative reaction pathway with a lower activation energy.

Factor	Effect on rate	Example
Increase in temperature	Rate increases	Faster cooking at high temperatures
Increase in concentration	Rate increases	More concentrated hydrogen peroxide: faster fizzing
Presence of a catalyst	Rate increases	Platinum catalyst in an exhaust pipe

Common misconception

Do not, under any circumstances, believe that a catalyst shifts the equilibrium or alters the final quantity of products formed: it merely changes the rate at which this is achieved. A catalyst accelerates both the forward and reverse reactions in equal measure, so that the final state (equilibrium) remains exactly the same.