Heat exchange and change in entropy are related.. dS=dQ/T. If the process is adiabatic then dQ=0 and change in entropy dS=0/T=0 or ΔS=∫dQ/T=∫0/T=0. So entropy is constant (S=constant) in reversible adiabatic process. It doesn't mean that the entropy of the system is 0, it means that the change...