This is the calculation for a iireversible process then why they have written g reversible hange (asota) during an a body b at higher

process. 1or lnC InfevCrsidie The exact calculation of total entropy change (ASota) during an irreversible process, e.g., when heat ows from a body B at higher temperature (12) to a body A at lower temperature (1) when brought in contact with it may be carried out as follows: Suppose the heat lost by the body B is represented as qirrev The flow of heat may be allowed to take place infinitesimally slowly so that it is absorbed by the body A reversible and isothermally at T which may be represented as qrev The entropy change of the body B will also depend only on q.e Hence, / re Entropy change of body B = T Cu Entropy change of body A = 4rev odotatabie T (minus sign indicates decrease in entropy while positive sign indicates increase) AS, -rev T T rev rev total The combined system and the surroundings is sometimes called as an isolated system. "The results aei secs. 2.6 and 2.7 are thus for the isolated system. **Negative sign with w has hren n