@stux Because mass is never converted to energy, not even in nuclear reactions.. E=mc2 tells you that energy **has** mass, and mass has energy. Basically mass can be manifested as matter or energy..

You can convert matter to energy but it makes no sense to say you convert mass to energy.

It talks about hydrogen explosions as converting mass to energy for example, that is flat out wrong.

Hydrogen bonds and oxygen bonds have a certain energy contained in them, that energy has some mass (which is in addition to any mass contributed by the matter itself). When an explosion happens those bonds break and form new H2O bonds which have less energy to them. The difference in energy has been released in the form of heat and light. So it has converted bond-energy into heat/light energy. The total amount of energy in the whole system (including the heat/light released) is exactly the same, the total amount of matter in the system is exactly the same, and therefore the total amount of mass of the system is exactly the same.

What happens however is that energy you released as heat and light doesnt stay on the water molecules you just created, they spread out onto other molecules and as light waves. So whatever mass that energy has is now sent flying out into the world.

So the water that you have as a result from the reaction will be infentesimally lower in mass than the hydrogen oxygen you started with. But at no point did a mass to energy "conversion" take place, that statement makes no sense in any context.

Even in a nuclear explosion you wont get a conversion of mass to energy, the total mass of the system will remain exactly the same. You will, however, get a conversion of matter into energy, which is what makes nuclear reactions unique.