Reversible vs irreversible expansion

[Cameron Hankins 3J]

For a reversible expansion, is the external pressure changing? Or just the internal pressure of the surroundings changing? Do the external and internal pressure have to match each other at the beginning of a reversible expansion? If so, does that mean if the pressure external and internal match in an expansion, that it cannot be irreversible. Also, for irreversible, the pressure internally just immediately changes to match the pressure external right? Thanks for any help.

[Shelby Yee 1J]

For reversible expansion, the external and internal pressures are initially the same. When the external pressure is changed an infinitesimally small amount, the system is allowed to do work until it reaches equilibrium. In this way (allowing the system to do work in an infinitely small amount of increments), the system is able to do the maximum amount of work. This differs from an irreversible process in which the external pressure and the internal pressure are different. When the system is allowed to react, the system will spontaneously expand/compress and will not do the same amount of work as it would if it were a reversible process.