Hi, everyone. i have several questions about thermodynamics which I just read. 1. Why does a reversible process require equilibrium of the system all the time? 2. Is every process reversible if it's very very slow so that the system is in equilibrium all the time( and there's no friction or some other factors that may dissipate the energy) ? 3. When we calculate the entropy (clausius definition of change in entropy)Why do we use the thermal energy transfered when the system had followed a reversible path? Because of the equilibrium state? Thanks!