Stories About Chemistry
46. The Magic Barrier
Hardly has hydrogen been mixed with oxygen than water vapour appears.
Hardly does an iron plate has come into contact with air than it becomes coated with reddish brown rust, and a few minutes later the solid lustrous metal has turned into a loose powder, iron oxide.
All the chemical reactions in the world proceed at a breath-taking speed. All molecules react with each other independent of the energy they possess. Each collision between two molecules results in their chemical union.
All the metals would disappear from the face of the Earth, because they would be oxidized. Complex organic substances, including those constituting living cells would change into simple, but more stable compounds.
It would be a strange world, a world without life, a world without chemistry, a fantastic world of very stable compounds with no inclination to enter into chemical reactions.
Fortunately no such nightmare threatens us.
There is a magic barrier which stands in the way of such a universal “chemical catastrophe.”
This barrier is known as activation energy. Molecules cannot enter into chemical reactions unless their energy equals or exceeds their activation energy.
Even at ordinary temperature there will be molecules, among those, say, of hydrogen and oxygen, with energies greater than or at least equal to their activation energy.
That is why water forms, though very slowly, under such conditions. The reaction is slow because the number of sufficiently energetic molecules is too small.
But a high temperature brings many molecules up to the activation barrier, and the number of instances of chemical interaction between hydrogen and oxygen grows enormously.