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phyzguy
#10
Feb13-12, 04:02 PM
P: 2,179
I don't have any way to calculate it other than what I said. Since I believe in relativity, I believe that E=mc^2. So if energy is given off, the reactants must have lost an amount of mass equal to E/c^2. Admittedly this effect is very small in chemical reactions. For example, take hydrogen, which has an energy content of about 120 MJ/kg, or 120 kJ/g. If I burn 1g of hydrogen together with 32g of oxygen, this will liberate 120 kJ Joules of energy. The resulting product (H2O) will weigh slightly less than 33g, by an amount 120kJ/c^2 = 1.3*10^-16 g. Obviously this is immeasurably small, but the situation is qualitatively the same as nuclear reactions. It's just the effect is large enough to measure in nuclear reactions.