To Phil: answer to Facebook question

At long last, I remember to answer your question, which I had completely forgotten.

"Ryan McMinn had a random thought: If matter changes its properties via chemical reactions, does energy change its properties via reactions?"

Not exactly. There is an apples-&-oranges issue here. Matter, in the sense of E=mc^2, means "mass", and mass itself does not change properties per se -- in chemistry, it itself is a property of all atomic or subatomic material, not explained by chemistry. In chemical reactions, mass itself does not change: you can either lose/gain mass from one system to the next, or mass can be converted to/from pure energy.
But this question isn't entirely off-the-mark. Energy can be converted to and from different forms, one of which is mass. Potential energy can be converted into kinetic energy, which could also be converted into mass; which could be converted into, say, "chemical" energy (e.g. the energy of atoms and molecules to combine together); which could also be lost in the form of friction. You haven't created or destroyed energy, you've just changed the form each time. That isn't the same thing as saying that you've changed the properties of energy, per se, you've just changed the properties through which energy is realized.
Which of course begs the question of what mass really is, and why is can be viewed as a form of energy... Heh-heh. I'll leave you at that for now.