Effect of concentration on chemical reactions

Free radicals are usually small groups or single atoms that have spare un-bonded electrons which are readily available for a chemical reaction. They are very shortlived items lasting less than a thousandth of a second but long enough to do harm to cells or produce a chemical reaction. 

In our bodies oxygen atoms, O, and small peroxide radicals are made as a byproduct of the respiration of carbohydrates, and these can do a lot of damage to living cells. The blood of our bodies is ready for this and contains enzymes that quickly deal with free radicals by reacting with them (see Section 6.3). 

The presence or absence of these free radicals can change the cell clock and affect the rate at which cells divide. The production of unwanted free radicals inside some cells makes them divide at a rapid rate. In these circumstances some cells make abnormal or cancerous growths. If there are too many free radicals the cells are killed altogether. 

Free radicals are made when a normal covalent bond splits in half with each atom receiving an equal share of the electron pairs. For example a hydrogen molecule H—H splits into two equal halves with each hydrogen atom receiving one electron, H. Covalent bonds that split in half in this way are said to break homolytically . Free radicals are often shown by having an asterisk on their formulae (see also Section 13.2). 

In 1997 there was an urgent phone call from a chemical works to the ambulance service. There had been an accident in the laboratory at the works. A flask had broken and the solution of phenol it contained had sprayed out onto the forearm of the worker. It was not much, but it was enough. The worker was, of course, not wearing goggles, nor a laboratory coat. Come on, it was summer - it was hot Tee-shirts were the order of the day. Anyway, it will never happen to me . 

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