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Clara Chung
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If a reservoir is in thermal contact with a system, why is the entropy simply Q/T ? Shouldn't this equation only valid for reversible process? Why is it reversible?
If the heat flow from the reservoir to another body is due to a finite temperature difference the process is not reversible. But ##\Delta S = \int dQ_{rev}/T## so you just have to find a reversible process between the initial and final state and work out the integral. The reversible process is one in which the same heat flow occurs at an infinitessimal temperature difference (eg. Insert a Carnot engine between the reservoir and body). [note: the reversible process between the initial and final states for each component will necessarily differ].Clara Chung said:If a reservoir is in thermal contact with a system, why is the entropy simply Q/T ? Shouldn't this equation only valid for reversible process? Why is it reversible?
In thermodynamics, an ideal constant temperature reservoir is defined as an entity for which the entropy change is always ##Q/T_R##. As such, one assumes that any irreversibility (and all entropy generation) takes place within the system, and none takes place within the reservoir. This means that the reservoir is implicitly assumed to have an infinite thermal conductivity and an infinite heat capacity, such that there are (a) never any temperature gradients within the reservoir and (b) its temperature never deviates from ##T_R## Thus, it always presents the temperature ##T_R## at its interface with the system.Clara Chung said:If a reservoir is in thermal contact with a system, why is the entropy simply Q/T ? Shouldn't this equation only valid for reversible process? Why is it reversible?
Entropy change in a reservoir refers to the change in the disorder or randomness of a system over time. In thermodynamics, it is a measure of the amount of energy in a system that is unavailable for work.
Entropy change in a reservoir can be calculated using the equation ΔS = Q/T, where ΔS is the change in entropy, Q is the heat energy added or removed from the system, and T is the temperature in Kelvin.
The factors that affect entropy change in a reservoir include the amount of heat added or removed from the system, the temperature of the system, and the nature of the substances involved in the process.
Entropy change is important in thermodynamics because it helps us understand the direction and efficiency of energy transfer in a system. It also plays a crucial role in the second law of thermodynamics, which states that the total entropy of a closed system will always increase over time.
In most cases, entropy change cannot be reversed. According to the second law of thermodynamics, the total entropy of a closed system will always increase. However, in some cases, such as in a reversible process, entropy change can be reversed.