In an isobaric process, how is it possible to be reversible. In the case that volume is decreased, lets say $2m^3$ to $1m^3$ (at infinitesimally small increments) at a constant $1$ MPa of pressure.
Heat must be extracted such that pressure does not increase in the system. There is a net transfer of heat, so why is it that this process is reversible?
Also in an adiabatic process, with a compression of $2m^3$ to $1m^3$ at a varying pressure. From the idea of adiabatic processes there is no transfer of heat.
So why can an irreversible adiabatic process exist(in an ideal system)?