Part Il 13. Consider two solid blocks, one hot and the other cold, brought into
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Question
Part Il 13. Consider two solid blocks, one hot and the other cold, brought into contact in an adiabatic container. After a while, thermal equilibrium is established in the container as a result of heat transfer. The first law requires that the amount of energy lost by the hot solid be require that the decrease in entropy of the hot solid be equal to the increase in entropy of the cold one? equal to the amount nt of energy gained by the cold one. Does the second la ener 14. Is a process that is internally reversible and adiabatic necessarily isentropic? Explain 15. The entropy of steam will (increase, decrease, remain the same) as it flows through an actual adiabatic turbine 16. What three different mechanisms can cause the entropy of a control volume to change? 17. A piston-cylinder device contains nitrogen gas. During a reversible, adiabatic process, the entropy of the nitrogen will (never, sometimes, always) increase 18. Does the cyclic integral of heat have to be zero (i.e., does a system have to reject as much heat as it receives to complete a cycle)? Explain. 19. A piston-cylinder device contains helium gas. During a reversible, isothermal process, the entropy of the helium will (never, sometimes, always) increase 20. The entropy of a hot baked potato decreases as it cools. Is this a violation of the increase of entropy principle? Explain 21. To determine the entropy change for an irreversible process between states 1 and 2 should the integral 12 dQ/T be performed along the actual process path or an imaginary reversible path? Explain. 22. During a heat transfer process, the entropy of a system (always, sometimes, never) increases. 23. Some properties of ideal gases such as internal energy and enthalpy vary with temperature only [that is, u u(T) and h h(T)] Is this also the case for entropy?Explanation / Answer
13) No. Because heat always transfers from hot body to cold body. Now if we think about definition of entropy as ration of heat transfer to temperature of body. Now if i say hot block as h and cold as c then Sh will be lower compared to Sc (Q lost from hot body is same as heat gained by cold) so Sh+Sc will be > 0.
14) Yes processes which are internally reversible and adiabatic are isentropic( i.e S= constant). Isentropic processes are ideal processes. When work transfer takes place without friction and no heat transfer takes place then that is isentropic process.
15) Entropy of steam as it flows through turbine actually increases. As work takes place in association with friction so entropy of steam increases(due to internal irreversibility).
16) 1. Heat transfer through CV 2. Stirring work without heat transfer(which increases temperature of fluid) 3. Internal irreversibility like friction
17) Reversible adiabatic processes are isentropic processes where entropy remains constant. Never increase.
18) No. For reversible processes cyclic integral of heat is equal to zero.
19) For expansion processes it can increase whereas for compression it decreases.
20) No as potato cools it transfer heat to surrounding medium colder than potato so entropy of system + surrounding will be >0 which is not violation.
21) As entropy is point function it depends on end states. So to determine entropy change for irreversible process we can assume reversible path and find entropy change.
22) Sometimes, it depends on whether heat is absorbed by system or rejected.
23) No,entropy is not function of only temperature.