⚾️honors physics review
Heat Reservoir
Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
A heat reservoir is an idealized concept in thermodynamics that represents a system with an infinitely large thermal capacity. It can be thought of as a source or sink of heat that can exchange energy with other systems without undergoing any significant change in its own temperature or internal energy.
5 Must Know Facts For Your Next Test
- The Second Law of Thermodynamics states that heat cannot spontaneously flow from a colder to a hotter object without work being done, and a heat reservoir is a key concept in understanding this law.
- Heat reservoirs are often used in the analysis of thermodynamic cycles, such as the Carnot cycle, to model the exchange of heat between the system and its surroundings.
- In an isothermal process, a system exchanges heat with a heat reservoir at a constant temperature, allowing for the conversion of heat into work or the reverse.
- The entropy of a system increases when heat flows from a hotter to a colder object, as the heat reservoir acts as an infinite sink or source of entropy.
- The concept of a heat reservoir is an idealization, as in reality, no system has an infinitely large thermal capacity, but it is a useful abstraction for understanding and analyzing thermodynamic systems.
Review Questions
- Explain how the concept of a heat reservoir is related to the Second Law of Thermodynamics.
- The Second Law of Thermodynamics states that heat cannot spontaneously flow from a colder to a hotter object without work being done. The concept of a heat reservoir, which can be thought of as an infinite source or sink of heat, is central to understanding this law. In a thermodynamic process, heat can flow from a hotter heat reservoir to a colder system, but not the reverse, without the input of work. This asymmetry in the flow of heat is a direct consequence of the Second Law and the role of heat reservoirs in maintaining temperature differences and enabling the conversion of heat into work.
- Describe the role of a heat reservoir in the analysis of thermodynamic cycles, such as the Carnot cycle.
- Heat reservoirs play a crucial role in the analysis of thermodynamic cycles, such as the Carnot cycle. In the Carnot cycle, the system exchanges heat with a hot heat reservoir during the isothermal expansion process and a cold heat reservoir during the isothermal compression process. The temperature difference between the hot and cold heat reservoirs determines the maximum theoretical efficiency of the Carnot cycle, as per the Carnot theorem. The heat reservoirs act as infinite sources or sinks of heat, allowing the system to undergo reversible, isothermal processes that are essential for the optimal performance of the thermodynamic cycle.
- Explain how the concept of a heat reservoir is related to the increase in entropy during the flow of heat from a hotter to a colder object.
- The concept of a heat reservoir is closely linked to the increase in entropy during the flow of heat from a hotter to a colder object, as described by the Second Law of Thermodynamics. When heat flows from a hotter heat reservoir to a colder system, the entropy of the universe (the system and the heat reservoir) increases. The heat reservoir, being an infinite source or sink of heat, can be considered to have a negligible change in entropy compared to the system receiving the heat. This allows the entropy of the universe to increase, as the system's entropy increases more than the heat reservoir's entropy decreases. The irreversible nature of this heat transfer process and the resulting increase in entropy is a fundamental aspect of the Second Law, which the concept of a heat reservoir helps to elucidate.