Reactions can be speeded up by:

1. Using reagents that are either:-

• more CONCENTRATED (for LIQUIDS) or
• at a higher PRESSURE (for GASES)

2. Increasing the TEMPERATURE at which a reaction occurs – generally for every 10^oC 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).

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.