Activation energy


Molecules travel at a slower average speed when temperatures are low. That is to say that not all molecules travel at the same speed but on average their speed is slower than during high temperatures. Click to see the difference.

When you open the gas tap natural gas, mainly methane, pours out and mixes with oxygen in the air. But the gas does not burst into flames unless a flame or spark is placed near the gas outlet.

When we use a match to light a fire we provide activation energy to the mixture of gas and oxygen.

For a chemical reaction to take place, reactant molecules need to collide with enough force to break bonds. Shown on the left are two molecules under normal conditions. Collisions occur but without the force needed to initiate a reaction.

In order for a reaction to occur molecules must collide with enough force to break the chemical bonds that hold them together. Energy, known as activation energy, must be supplied to increase the kinetic energy of the reactant molecules and cause violent collisions.

Take hydrogen and oxygen for example. The energy present at normal room temperatures is not enough to speed up the molecules to any degree. We have to supply a flame or some other form of energy to excite the molecules enough so that they collide with extreme force.



Click to see a FLASH animation of the reaction below.

What is activation energy?
The more gas that is present the more matches you would need to start the fire:

The more gas and oxygen that is present the greater the amount of energy released

Before a match is added to the methane and oxygen mixture no collisions are taking place between methane and oxygen molecules.

The energy from the match is absorbed by the molecules to create a solid substance

Activation energy is always present in the atmosphere to cause gas molecules to react