Reversibility
A reversible process is one that can be reversed without changes to the system or its surroundings (Wikipedia). A reversible process occurs in infinitesimally small steps such that the system never leaves thermodynamic equilibrium. For this to occur, any process would take an infinite amount of time to complete; it would not appear to be occurring.
In a truly reversible process, there is no heat lost to the surroundings by the system. For this reason, the energy produced by the system is maximized. A reversible cycle will be as efficient as possible.
It is impossible to achieve a reversible cycle in real life; heat is always lost to the surroundings with a significant source of heat generation being friction.
One example of a reversible process is adding sand to a scale one grain at a time. Because the mass of a single grain of sand is so small, the mass being read by the scale would not cause a noticeable change in the scale's reading. The scale would not fluctuate before reaching equilibrium, as it would had something of a greater mass been added. Adding a single grain of sand at a time allows the scale to remain in a pseudo equilibrium.
Classroom Reversibility
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