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.