Why is the maximum work of a system never obtained from a real process?

The maximum work obtainable from a system is associated with ideal processes that are reversible and conducted under equilibrium conditions. In contrast, real processes are typically irreversible due to various factors, such as friction, turbulence, or non-equilibrium conditions. This irreversibility inherently involves energy dissipation, often as heat, and as a result, the work done by the system is always less than the maximum potential work.

In thermodynamic contexts, irreversible processes reflect a loss of useful work capacity, contrasting with reversible processes where the system can operate in a manner that ensures no energy is wasted. This difference is rooted in the second law of thermodynamics, which states that the entropy of an isolated system only increases over time. Consequently, the presence of irreversibilities limits the efficiency with which a system can convert its internal energy into work.

While spontaneous processes and heat production do occur in real contexts, they do not provide the primary reason for the limitation on maximum work. Instead, it is the nature of the irreversible process that fundamentally restricts achieving that theoretical maximum work from real systems.