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• When two molecules of hydrogen combine with one molecule of oxygen to form two water molecules,
2H2 + O2 → 2H2O
the energy released is 5 eV. (a) What is the mass difference between the three original molecules and the two final ones? (b) Given that the water molecule has mass about 3 × 10−26 kg, what is the fractional change in mass, ΔM/(total mass)? (Does it matter significantly whether you use the initial or final total mass?) (c) If one were to form 10 g of water by this process, what would be the total change in rest mass?
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