So it has to obey the first law of thermodynamics that basically states that energy is never created, energy is never destroyed. Energy can only be transformed from one form to another. So the total amount of energy in our universe is always constant. We also have to remember the second law of thermodynamics which basically describes the fact that in any real biological process the change in entropy of the universe is always positive, it always increases. So we also have to consider the temperature and the conditions under which a reaction is taking place because under certain conditions a reaction might be spontaneous but under other conditions the reaction might not be spontaneous. And so we have to consider the gifts free energy of our reaction.