Is there ever a loss of mass from the release of energy resulting from
a chemical reaction? For example is any mass lost from the consumption
of fuel by a fire?

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Request for Question Clarification by mathtalk-ga on 02 Nov 2003 16:00 PST

Hi, epunderwood-ga:

Benny1979-ga's comment is correct.  The yield of potential energy from
a chemical reaction results in the decrease in mass predicted by E =
mc^2.

However the mass loss is correspondingly slight, so much so as to be
immeasurable by current techniques.

If you like, a Researcher might post as an Answer the details for the
theoretical loss of mass resulting from (say) the reaction of 2 moles
of H2 and one mole of O2, yielding 2 moles of water.

regards, mathtalk-ga

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Request for Question Clarification by mvguy-ga on 03 Nov 2003 15:29 PST

What information do you need that isn't included in my answer to a
previous question?  Thanks!
http://answers.google.com/answers/threadview?id=76608

Yes a loss of mass does occur. 
For heat to be given out more energy is given out when bonds form (The
C=O) than required to break the other bonds. These new molecules
formed are at a lower energy state (More stable) and thus weigh less.

I don't have the time now to answer this question (maybe later if no
one else does). But you'll find in this answer of mine the basis of
the answer to the current question:
http://answers.google.com/answers/threadview?id=76608

The answer is yes.  The fuel combines with oxygen and the weight of
the burnt products (mostly carbon dioxide and water) is less that the
original weight of the fuel plus the oxygen by the exact amount of the
energy released.

For example burning  1 ton of fuel oil releases 41,868,000 kilojoules of energy.

From E=MC^2

and entering E in joules, C in Meters/sec, for M in kg

the mass loss is 

M=E/C^2=41,868,000,000/(3*10^8)^2 Kg=0.0000004652 kg

or 0.0004652 grams

Not much considering you started with a ton of fuel and a substantial
mass of oxygen!!!