The Standing Invitation

Posts Tagged ‘Cancer

Microwave Cooking

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It much less common these days, but you do still occasionally hear stories about mobile phones causing cancer. They probably don’t, by the way – see references. But the issue is a convenient gateway into another of the unsolved problems of chemistry, a problem to do with microwaves.

Mobile phones are microwave emitters. The question of mobile phones and cancer is really a question about the role of microwaves in biochemistry. Do microwaves interfere with chemical reactions?

We know that infrared radiation, as emitted by hot things, can interfere with or even cause chemical reactions – we demonstrate this every time we cook a meal. The pizza that just burned in my oven underwent several infrared-initiated chemical reactions, most of them undesirable. This happened because photons of infrared radiation are able to break chemical bonds; they forced the molecules in my pizza to reconfigure themselves, generating smoke and steam and ruining my meal in the process.

When it comes to microwaves, what we are looking for is called a specific microwave effect (SME) – some chemical process that occurs only as a result of the microwaves, and cannot be explained in any other way.

Microwave photons are much less energetic than infrared. They do not have the strength to break chemical bonds. They can move electrons around within the molecule, causing them to rotate very quickly, but there simply isn’t enough energy to do any chemistry.

So when you irradiate a sample with microwaves, you would not expect any chemical reactions to take place. But they do. What is happening?

The answer is that the microwaves are causing the molecules to rotate, which in turn generates heat through something akin to friction. This heat does have the energy to break bonds – and so we’re back to chemical reactions caused by thermal effects. So although the microwaves are causing the chemistry, it’s only through normal, boring heating.

But that doesn’t quite explain everything. Sometimes, heating a reaction in the conventional way gives one product, but blasting it with microwaves generates another. Are these examples of SMEs?

Probably not. There is a difference between heating something directly with infrared and heating it indirectly with microwaves: heating with infrared works from the outside in. If you heat a vessel, the surface gets hot first, and a lot of the heat just gets radiated off to the air. Microwave heating works from the inside out, which allows much higher temperatures to be reached inside the vessel. This can have an effect on the chemistry – but it’s still heat that’s doing things; it’s not an SME.

The existence of true SMEs is still much debated. Can all the quirky chemical effects of microwave irradiation be attributed to thermal heating? No, not yet, but we’re working on it. Maybe someday an exception will be found, and that will be very exciting; but for now there is no solid evidence that a microwave emitter like a mobile phone has any more capacity to change your body chemistry than simply being outside on a hot day.


Written by The S I

August 1, 2011 at 8:30 pm