Common Reactions, Energy, Reaction Speed

There are many different types of chemical reaction. The table shows some common reaction types, with examples. 

With oxygen, a substance might:

• React rapidly, burning and producing heat and light. This is combustion.

• React slowly, when water is also present, and form an oxide coating. This is corrosion.

Most metals corrode. A special case is when iron corrodes - the process is called rusting. 

Chemical reactions occur at different speeds. For example, it takes many years for a garden spade to rust away, but a piece of paper on fire burns away in only a few seconds. During any reaction, the reactant particles react together when they collide into each other. This means that we can do several things to make a reaction go faster. 

Increase the Temperature

By making the reactants hotter, we make the particles move around much more quickly, so they crash into eeach other and react. E.g. Steak cooks faster when the stove element is set to 'high' rather than 'medium', because the higher temperature makes the meat particles react more quickly and turn brown. 

Increase the Amounts of Reactants

By squeezing more reactant particles into the mixture (through using a higher concentration), we make many more collisions happen, so there is a faster reaction. E.g. blowing on fireplace embers makes them burn faster because you are adding more oxygen reactant. 

Use Smaller Particles (or Larger Surface Area)

This means ther eare more surfaces for the reactant particles to collide with, so more react and the reaction takes place more quickly. E.g. kindling burns much faster than a large block of firewood does, because kindling has more surface on which the combution reaction can occur. 

Use a Catalyst

A catalyst is a substance that speeds up a reaction without itself being used up. It works by helping the reactant particles line up the right way for the collisions that cause the reaction, so more particles can react and the reaction takes place more quickly. A catalytic converter on a car's exhaust sstem contains platinum, palladium and rhodium metals to speed up the reactions that deactivate dangerous exhaust gases.