I was studying some basic thermodynamics concepts and I noticed that in reversible processes in my book always the adiabatic word is used.

1. So are all reversible processes adiabatic? (ques 1)

2. Or are at least all reversible expansion adiabatic? (ques 2),

3. And are all irreversible processes adiabatic? (ques 3)

4. or at least all irreversible expansion are adiabatic? (ques 4)

5. If all of these statements are wrong then when are they true?

6. This adiabatic word is troubling me very much as it is almost used everwhere. Why?

I know adiabatic means $Q=0$ (that is the system does not exchange heat energy with the surrounding) so no need to explain adiabatic.

• All right, a process is called quasistatic if all the parameters of the system$(p,V,T,etc)$ vary physically indefinitely slowly so that the system is found all the time in an equilibrium state. This means that at any stage of the process, there will be enough time for the parameters to equalize over the entire system and such a process will represent a continuous succession of equilibrium states infinitely close to each other. They are practically quasi-equilibrium or quasi-static. – Rajesh Sardar Oct 14 '15 at 16:19