How to speed up a chemical reaction

Last week we tried a simple chemical reaction to investigate alka seltzer reacting with water. We’ve also observed the reaction between baking soda and vinegar before, both of which are very safe for even young children to observe.

Taking this a step further we’re going to investigate how to speed up a chemical reaction, while still keeping things very basic and easy to understand.

The nature of the reactants

Reactants are the two substances you combine to get the reaction. Some react slowly and some much faster depending on the bonds that need to be broken. For example, gold is very unreactive, while sodium and potassium are so reactive that they tarnish instantly when exposed to the air.

Particle Size

The smaller the particles the faster the reaction, this is because there is a larger surface area available to react with the other substance.


The higher the concentration, the faster the reaction, this is because there is more of the reactive substance available to react. We’ve observed this very simply in the past by adding more alka seltzer to a lava lamp which gives a bigger and faster reaction.


The higher the temperature the faster the reaction, this is because if you heat up a substance the particles have more energy and move around faster meaning they have more contact with the other reactive substance.

We’ve designed a very simple experiment to demonstrate this using alka seltzer and hot and cold water.

Please be careful when trying this at home that the water you use isn’t too hot as it could spill out or burst the balloon, especially if you use a smaller container.

How to speed up a chemical reaction


Can you guess which of these four jars contained the warmest water?


A Catalyst is a substance that speeds up a chemical reaction but is not changed itself by the reaction and can be used again. Examples of catalysts include platinium which is used in car exhausts to break down harmful emissions and yeast is a biological catalyst that speeds up the process of fermentation.

The opposite effect is demonstrated by food in a fridge, the cooler temperature slows down the reaction between oxygen and bacteria that makes the food spoil. Keeping your food fresher for longer.

Suitable for Key Stage 3 – Chemical Reactions

How to speed up a chemical reaction

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