Factors Affecting Rates of Reaction

• The rate of reaction depends on 4 things: Temperature, the concentration of a solution or the pressure of gas, surface area - this changes depending on the size of the lumps of a solid, and the presence of a catalyst
• More collisions increases the rate of reaction
• All 4 methods of increasing the rate of a reaction can be explained in terms of increasing the number of successful collisions between the reacting particles
• Increasing the temperature increases the rate
• Temperature: When the temperature is increased, the particles all move faster. If they're moving faster, they're going to collide more frequently
• Temperature: The faster the particles move the more energy they have, so more of the collisions will have enough energy to make the reaction happen
• Increasing the concentration or pressure increases the rate
• Concentration/Pressure: If a solution is made more concentrated, it means there are more particles knocking about in the same volume of water (or other solvent)
• Concentration/Pressure: Similarly, when the pressure of a gas is increased, it means that the same number of particles occupies a smaller space
• Concentration/Pressure: This makes collisions between the reactant particles more frequent
• Increasing the surface area increases the rate
• Surface area: If one of the reactants is a solid, then breaking it up into smaller pieces will increase its surface area to volume ratio
• Surface area: This means that for the same volume of a solid, the particles around it will have more area to work on - so there will be collisions more frequently
• Using a catalyst increases the rate
• Catalyst: A catalyst is a substance that speeds up a reaction, without being used up in the reaction itself. This means it's not part of the overall reaction equation
• Catalyst: Different catalysts are needed for different reactions, but they all work by decreasing the activation energy needed for the reaction to occur.
• Catalyst: Catalysts provide an alternate reaction pathway with a lower activation energy
• Catalyst: Enzymes are biological catalysts - they catalyse reactions in living things
• This is called a reaction profile