Reversible Vs Irreversible

[joycelee1A]

Why is the temperature constant in reversible reactions whereas temperature changes along the path for irreversible reactions?

[Sue Xu 2K]

For reversible expansion, it is isothermal because the system does work and lose energy, and then the loss of energy is replaced by the heat flow into the system. So U, the internal energy, remains constant. For U = 3/2 nRT, T also stays constant.

[Michael Cheng 1C]

So then why is temperature not constant in irreversible reactions?

[Kevin Tabibian 1A]

I believe that being at thermodynamic equilibrium (constant heat) is part of the definition of a reversible reaction whereas it is not required for irreversible.