Final answer:
Real reactions typically involve an increase in entropy, making them irreversible due to the second law of thermodynamics, which states that the total entropy of an isolated system will never decrease over time in spontaneous processes. This increase in entropy also indicates less energy availability for work in the system.
Step-by-step explanation:
The question posed is: In regard to free energy, why are real reactions irreversible? The answer to that is because real reactions typically involve an increase in entropy of the system. An irreversible process is one where the system changes in such a way that the process cannot simply be reversed by an infinitesimal modification of a variable. This usually coincides with the transfer of heat to the surroundings, leading to an increase in chaos or disorder within the system.
It's important to note that, according to the second law of thermodynamics, the total entropy of an isolated system can never decrease over time for any spontaneous process, which aligns with the statement that all spontaneous reactions result in the increased total entropy of a system. For example, when ice melts into water, the entropy increases because the highly ordered solid structure is converted into a disorderly liquid, and thus the system becomes more chaotic.
Moreover, entropy is linked to the concept of the unavailability of energy to do work. As entropy increases in a system, it signifies a lesser degree of the system's energy being available for doing work, because some of this energy is inevitably dispersed in the form of heat to the environment.