Reversible vs. Irreversible Reaction

[Mike Matthews 1D]

Hi,
Could someone please clarify the difference between a reversible and an irreversible reaction. Also why is the work done during a reversible expansion of a gas the maximum expansion work possible?
Thanks.

[Kyle Sheu 1C]

In a reversible reaction, an infinitesimally small change in the independent variable reverses the direction of the reaction. In an irreversible reaction, the same change would have no effect on the direction of the reaction.

During a reversible reaction, the changes are extremely small, and when applied in series, result in a continuum of values (think of a continuous function--graphically speaking).
Calculus-wise, this would be the equivalent of an integral. If we are to continue the calculus analogy for an irreversible reaction, think of it as an under-approximation.

Using the example in Fig 8.6 and 8.7 in the book, think of it as: for every 1 unit of volume change, the system experiences less than maximum resistance from external pressure.

[Janine Chan 2K]

Also, reversible reactions occur slowly, while irreversible reactions occur quickly. So, if the process is reversible (done slowly), minimal energy is lost to the surrounding as heat, allowing for maximum expansion work.