View the video on the right.
In a mixture of methane and oxygen molecules no collisions occur between the two different molecules.
Activation energy is the energy needed to
In an exothermic reaction energy is
In an endothermic reaction energy is
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. This energy is represented
as a small peak on the energy profile diagram shown below.
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.
The animation below shows the
relative speeds of the molecules prior to the activation energy been supplied.
Energy is given off because the product molecules contain less energy
than the reactant molecules.
Click to see
a FLASH animation of the reaction below.
