# Heat exchange after thermal equilibrium

• B
• vcsharp2003
In summary, the conversation discusses the exchange of energy between three systems, A, B, and C. Initially, A and B are separated by an adiabatic wall while each exchanges energy with C through a diathermic wall. Once A and B reach thermal equilibrium with C, they are allowed to exchange energy through a diathermic wall, while energy exchange between A and C and B and C is prevented by an adiabatic wall. The 0th law of thermodynamics states that systems in thermal equilibrium should not exchange heat energy, but this can happen in certain circumstances, such as with expandable ideal gas systems at different pressures joined by a movable piston through a diathermic wall. The conversation also mentions that while
vcsharp2003
TL;DR Summary
Can there be any heat exchange between two systems that are in thermal equilibrium?
In screenshot below, systems A and B are separated by an adiabatic wall initially while each of them exchanges energy with system C via a diathermic wall. Once A and B reach thermal equilibrium with C, then A,B are allowed energy exchange via a diathermic wall, and energy exchange between A and C as well as B and C is prevented by using an adiabatic wall.

To my knowledge systems that are in thermal equilibrium should not exchange heat energy. Is this true or they could exchange heat depending on circumstances? May be expandable ideal gas systems at different pressures and joined by a common diathermic movable piston could exchange heat as the piston moves from high pressure side moves towards the lower pressure side.

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The 0th law of thermodynamics states that if A is in thermal equilibrium with C and B is in thermal equilibrium with C, then A is in thermal equilibrium with B. My guess is that the figure is used to illustrate this principle.

Note that while there is no net exchange of heat energy between two systems in equilibrium (2nd law), there are energy fluctuations (A and B will exchange energy back and forth, and this averages to 0). For a large enough system (or in the thermodynamic limit), these fluctuations are too small to be measured.

vcsharp2003
DrClaude said:
My guess is that the figure is used to illustrate this principle.
Yes, this was a diagram used to explain Zeroth Law of Thermodynamics in the textbook.

Thankyou for the detailed answer. It's clear to me now.

## 1. How does heat exchange occur after thermal equilibrium is reached?

After thermal equilibrium is reached, heat exchange occurs through the process of conduction, convection, and radiation. In conduction, heat is transferred through direct contact between two objects. In convection, heat is transferred through the movement of fluids or gases. In radiation, heat is transferred through electromagnetic waves.

## 2. What factors affect the rate of heat exchange after thermal equilibrium?

The rate of heat exchange after thermal equilibrium is affected by several factors, including the temperature difference between the two objects, the surface area of the objects, and the type of material the objects are made of. Other factors such as air flow and insulation can also affect the rate of heat exchange.

## 3. How does heat exchange impact the temperature of the objects involved?

During heat exchange, heat will flow from the object with a higher temperature to the object with a lower temperature until both objects reach the same temperature. This means that the temperature of the objects involved will change as heat is transferred between them.

## 4. What is the role of thermal equilibrium in heat exchange?

Thermal equilibrium is the state in which two objects have reached the same temperature and there is no longer a net flow of heat between them. In heat exchange, thermal equilibrium is important because it ensures that both objects reach the same temperature, resulting in a balanced and stable system.

## 5. How is heat exchange after thermal equilibrium related to the laws of thermodynamics?

Heat exchange after thermal equilibrium is governed by the second law of thermodynamics, which states that heat will naturally flow from a higher temperature to a lower temperature until thermal equilibrium is reached. This law also explains why it is not possible for heat to flow from a colder object to a hotter object without the input of external energy.

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