- Concentrations of reactants (the number of colliding particles in unit volume)
- Pressure for gas reactions (the number of colliding particles in unit volume)
- Surface area of solid reactants
CONCENTRATION or PRESSURE
The particles collide more often (the collision frequency is higher) with more particles in a certain volume and therefore there is greater chance of a successful collision (i.e. one that results in a reaction) occurring in a certain time.
For aqueous solutions:
For the reaction of calcium carbonate with hydrochloric acid:
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)
As the temperature is increased,
- average kinetic energy of particles increases,
- average velocity of particles increases,
- the number of reacting particles possess the necessary activation energy increases.
- the rate of reaction increases.
SURFACE AREA OF SOLID REACTANT
Reactions generally only occur at the surface of a solid. Making a solid more finely crushed increases the surface area and therefore the number of particles exposed at the surface.
Then, there is a greater chance of the other reactant colliding with this particle on the surface and reaction occurring.
- is a substance that increases the rate of reaction without itself being used up in the reaction.
- acts by allowing the reaction to proceed by an alternative pathway of lower activation energy.
- is often written above the reaction arrow and does not appear in the chemical equation because it does not change in the reaction.
When a catalyst is used in a particular reaction, the Maxwell–Boltzmann distribution curve also shows how a lower activation energy results in a faster reaction.