MadSci Network: Chemistry

Re: Can a household microwave produce free radicals?

Date: Wed Jun 14 10:01:12 2000
Posted By: Rick Cousins, Regional Mgr/Chemist-Industry
Area of science: Chemistry
ID: 960311115.Ch

Microwaves heat thru two simple mechanisms. For molecules with a dipole 
moment, rotational energy is imparted. For free ions, a vibrational 
pattern is set up.  The energy of microwave generated by home cooking units
is not adequate to break bonds, just to spin up the molecules and allow
them to collide, producing heat.

For instance the energy of microwaves at the standard frequency of 2.45 
GHz is only 0.0016 ev. This is not even strong enough to break the weak
hydrogen bond (bond energy of 0.21 ev), much less a real bond such as the 
carbon-carbon single bond in ethane with has a bond energy of 3.8 ev.

Free radicals can still be produced by spontaneous decomposition or 
other processes. But the fact that the heating is done by microwave vs
convection heating will have no impact on the generation of free radicals 
per se.

There is one other consideration. With microwave heating of a food in a 
microwave transparent container, the food is always hotter than the 
container since the container is only heated by heat transfer from the 
food. But in conventional heating, the container may be much hotter than 
the food leading to superheating, burning, etc. This might be more likely 
to produce free radicals and other dangerous compounds. Consider a outdoor 
cooking grill as well for excessive heating.

Hope this helps.

--Rick (some information provided by CEM Corp, 
laboratory microwaves)

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