Rates of reactions

2P9: Friday 19th November

How do chemical reactions happen?• When particles collide / bump together, they

can react and become chemically joined. This is how chemical reactions happen.

Chemical reactions can occur at different speeds

Reaction SLOW MEDIUM FAST

Oil forming

Firework Exploding

Logs burning

Frying an egg

Experiment

• Aim: To see what effect the particle size has on the speed of a chemical reaction.

Weigh marble chips/powder

• Put a piece of filter paper on the top of your balance and turn on

• Measure out approximately 2g of marble chips – put to side for your experiment

• Using a new piece of filter paper on the scales:• Measure out the same weight of the

powdered calcium carbonate (chalk powder) using the spatula onto the filter paper

Method: Collect 2 small beakers and fill each with 25cm3 of hydrochloric acid.

Add the calcium carbonate to each beaker as shown above. Observe and record what happens.

Results:The calcium carbonate powder reacted faster than the lumps.

WHY???

• A quick explanation:Imagine you had a square which would be like a large particle. The other particle would only be able to hit off 4 sides - there is a small surface area.

• Watch the animation which follows…

• If we break the large square up into many smaller squares (smaller particle size) then there are many more surfaces for the other particle to hit, increasing the chance of a chemical reaction…

• Watch the following animation…

Conclusion

• The smaller the particle size, the faster the speed of the reaction

• When the particles are smaller, there is a greater surface area of the solid exposed to the acid. More of the particles are able to collide and so the reaction happens faster.