Although the universe is constantly expanding, it should still be considered a closed system considering the fact that at every moment there is a limited amount of space and matter within it.
Therefore the ratio of energy within the system should be limited to a certain degree. If you think about the idea of endothermic and exothermic reactions then there should be some ratio of total energy contained within all matter or reactions and total free energy.
If this is true, then is there some point in the future when all total free energy is contained within matter and therefore there is no longer movement of energy within the system and therefore no reactions, ultimately resulting in a complete standstill of all that is?