SPEEDIN G UP and SLOWING DOWN rates of reaction. Reactions can be speeded up by: 1. Using reagents that are either:- more CONCENTRATED (for LIQUIDS) or at a higher PRESSURE (for GASES) (THIS IS NOT THE SAME AS USING MORE REAGENTS) 2. Increasing the TEMPERATURE at which a reaction occurs – generally for every 10oC rise in temperature the reaction rate doubles. 3. Using reagents that are finely divided – POWDERS generally work faster than LUMPS. They have a BIGGER SURFACE AREA. 4. Using a CATALYST – this can generally speed up or slow down the rate at which a chemical reaction occurs. Reactions can be slowed down by: 1. Using reagents that are either:- more DILUTE i.e add lots of water (for LIQUIDS) or at a lower PRESSURE i.e use a large container (for GASES). (THIS IS NOT THE SAME AS USING LESS REAGENTS) 2. Reducing the TEMPERATURE at which a reaction occurs i.e COOL things down. 3. Using reagents that have a SMALL SURFACE AREA i.e the substance is in large lumps. 4. Using a CATALYST – the right catalyst can slow down the rate at which a chemical reaction occurs. EXPLANATION: THE COLLISION THEORY If the particles making up the substances are to react with one another they must hit each other hard enough in the right place. If both things occur the collision is said to be effective. So NO reaction will occur if: the particles are moving slowly. they don't hit each other in the right place. No reaction will be seen to occur if not enough particles react. Reactions generally slow down as the reaction proceeds because: the number of reacting particles available become smaller and smaller it takes longer for these reacting particles to meet one another and react.