State and explain the Kelvin-Planck statement of the second law of thermodynamics
The Correct Answer and Explanation is :
Kelvin-Planck Statement of the Second Law of Thermodynamics
The Kelvin-Planck statement of the second law of thermodynamics states:
“It is impossible for any device that operates in a cyclic process to receive heat from a single reservoir and convert it entirely into work. There must always be some waste heat rejected to a second reservoir.”
Explanation:
The Kelvin-Planck statement essentially tells us that no heat engine can be 100% efficient. In any cyclic process where heat is absorbed from a high-temperature source (reservoir), a portion of this heat must inevitably be lost to a cooler temperature sink (reservoir) when the system performs work. This is an intrinsic limitation on the efficiency of heat engines.
This statement directly contradicts the idea of a perfect heat engine, which would ideally convert all heat energy into useful work. If such an engine existed, it would be a violation of the second law of thermodynamics because it would essentially create energy from nothing, which is not possible in a real physical system.
The reason behind this limitation lies in the nature of thermodynamic processes. During the conversion of heat into work, some energy inevitably disperses into the surroundings due to factors such as friction, heat conduction, and entropy generation. This results in the need for a second heat reservoir to absorb the waste heat. In practical terms, this is why no engine is completely efficient.
The second law, which is fundamental to thermodynamics, dictates the direction of natural processes. It introduces the concept of entropy, a measure of disorder in a system. Entropy tends to increase over time in an isolated system, meaning that there is always a tendency for energy to spread out and become less useful for doing work. As a result, the efficiency of heat engines is constrained by this inevitable dissipation of energy.
In short, the Kelvin-Planck statement reinforces the principle that some energy in a system will always be unavailable for conversion to work, establishing limits to the performance of heat engines.
Let me generate an image to illustrate this concept for you.
Here is the diagram illustrating the Kelvin-Planck statement of the second law of thermodynamics. It shows a heat engine in a cyclic process where heat is absorbed from a high-temperature reservoir and converted into work, with waste heat being rejected to a cooler reservoir. The image highlights that not all heat energy is converted into work, which aligns with the principle that some energy must always be lost in the process. Let me know if you need further clarification!