Can you measure the mass of a chemical reaction?

Let's say you have CH₄ and of 2O₂ in a beaker and you measure the the total mass in the beaker.

You then burn these two substances and get two new substances in the form of CO₂ and 2H₂O.

Light and heat quite naturally escape from the beaker.

Do the resultant substances weigh less than the starting substances by a small amount?

Or do they weigh the same because invariant mass of the electrons, protons, and neutrons don't change by rearrangement?



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