usually, entropy change in solid and liquid is formulated as Cp(or Cv)ln(T2/T1) or Q/T(integral)+ Sgen. so, considering the former and the latter equations, Do their entropy changes include irreversibility due to Sgen? And next question, reservoir has no change in temperature and volume. therefore, its'entropy change is zero. (According to this formula: dS=Cvln(T2/T1)+Rln(V2/V1) ) but when we solve many matters in thermodynamics especially in entropy part, we think that the reservoir exchanging the heat with another part has the entropy change expressed as Q/T not zero. why is that?