Engineering Thermodynamics
In order that a cycle be reversible, following must be satisfied

Free expansion or friction resisted expansion/compression process should not be encountered
When heat is being absorbed, temperature of hot source and working substance should be same
When beat is being rejected, temperature of cold source and working substance should be same
All of these

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Engineering Thermodynamics
An isolated system is one in which

Mass does not cross boundaries of the system, though energy may do so
Neither mass nor energy crosses the boundaries of the system
Mass crosses the boundary but not the energy
Both energy and mass cross the boundaries of the system

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