4.18 describe the effects of changes in surface area of a solid, concentration of solutions, pressure of gases, temperature and the use of a catalyst on the rate of reaction

NOTE: this point is just about the changes that occur, if you want/need to understand why these changes occur, go to this point... 4.20


Changes in surface area
The bigger the surface area (to volume ratio) the faster the reaction. This is because there are more particles on the surface for the reactants to react with.  In a solid, to increase the surface area without decreasing the mass just break up the solid into smaller pieces.

Concentration of solutions
If a solution is very concentrated there are lots of particles for its volume (the particles are close together). Alternatively, if the concentration is very weak there are a very little amount of particles for its volume (the particles are very spaced out). 

Pressure of gases
This is very similar to concentration of solutions. If the gas is at high pressure there will be more particles squished into a certain space, more particles means a faster rate of reaction. Alternatively, low pressure results in little amount of particles meaning a slower rate of reaction.

Temperature
The hotter the reactants the faster the reaction. Alternatively, the colder the temperature of the reactants the slower the reaction rate. This is because the particles have very little energy. 

Catalyst
A catalyst works by giving the reactants a surface to 'stick' to. This will increase the rate of reaction.