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SPEEDING UP and SLOWING DOWN rates of reaction

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					     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.

				
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posted:4/7/2010
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