Is Thermal Equilibrium A System: 7 Facts You Should Know

Thermal equilibrium is a condition of a system and a surrounding to be in a state of temperature equilibrium. In this article, we are going to discuss how is thermal equilibrium a system.

Every object tends to acquire a thermal equilibrium state by emitting its internal heat into the surroundings or by acquiring the heat from the surrounding. The thermal equilibrium is a system when a system is in an isolated state.

What is thermal equilibrium?

The thermal equilibrium is a state of a system reaching a point where the temperature of a system matches the temperature of a surrounding.

A thermal equilibrium is a condition at which the flow of heat energy from a system to a surrounding stop and a system and surrounding has an equal temperature. The heat transfers from high energy level to the low temperature zone.

If two systems are in a thermal equilibrium state, then the third state in contact with these two systems will also be in a thermal equilibrium state. This is stated in the Zeroth law of thermodynamics.

Why is thermal equilibrium a system?

A system is in thermal equilibrium when there is no emission of heat from the system into the surrounding, not it takes heat from the surrounding.

A thermal equilibrium system is completely isolated from the surrounding. This type of system does not lose its mass but only the heat transmission can take place. As the system acquires the thermal equilibrium position the flow of heat stops.

Any system will tend to increase its internal energy if there is a heat supply to the system. For example, on supplying heat to the container of the water, the temperature of the water will go on increasing with time. If the heat supply is turned off, then the same volume of water will emit its heat in the surroundings and thus cooling down with time.

When a system is at thermal equilibrium?

A system is at thermal equilibrium when its internal temperature matches the external temperature of the surrounding.

There is no flow of energy from either side between the system and the surrounding. The temperature remains constant for both. Also, there is no transmission of matter from the system.

The two systems having differences in temperatures are kept together in contact, then there will be a transmission of heat from the hot point to the low temperature point. This heat flow will continue until both systems acquire the same amount of internal heat energy. This state of a system is called a thermal equilibrium state of a system.

Is thermal equilibrium a closed system?

A thermal equilibrium takes place only in the case of closed systems or two bodies in which only the heat energy can be transferred and not the matter.

A thermal equilibrium basically deals with the temperature of a system and how it is synchronized with the surrounding matter. If the temperature of a system is high than the surrounding, the matter from the surrounding grasp the heat from the system, and vice versa.

For a system to attain a thermal equilibrium state, there must be a flow of heat only. If there is a flow of matter only, then the heat that per mol of matter acquires will remain with the mass of matter only. And if there is a flow of matter and heat also, then no system would have been able to acquire a thermal equilibrium state.

Every time a new matter would have flown to a system that might have variable temperature as compared to the system. A system takes a time to acquire the state of equilibrium by the flow of heat.

Can thermal equilibrium occur in an open system?

A system that is not bounded by the walls and isolated from the surrounding is called an open system.

The open systems are unable to attain a state of equilibrium. In an open system, there is not only the exchange of heat but also the matter. The volume of matter transfers from the surroundings to the system.

The heat can be easily exchanged from the system to the surrounding in the case of an open system. But, the system will never be able to attain the position of equilibrium. This is because the mass is continuously exchanged from the system to the surroundings and along with the mass the heat is also given away from the system.

The new amount of mass added either lowers the total heat energy of the system or increases, and the process continues. But, in some parts, the open system also plays a major role to bring the system to the thermal equilibrium state.

How thermal equilibrium occurs in an open system?

The thermal equilibrium may occur in some scenarios and on large scale in an open system.

The heat energy always flows from the higher temperature region to the low temperature region. This is the factuality of any system in a surrounding. If an open system has high energy compared to the surrounding, then the heat will be transmitted to the surrounding from the system to acquire the equilibrium state.

A simple example here would be the exchange of air from high temperature regions to cold areas. The air flows from one region to another locality through the exchange of matter as well as heat energy. That is why the wind blows and the air hot air cools down. On the contrary, the heat energy is also acquired by the cold air, inevitable for the thermal equilibrium.

Another example that we can discuss here is the combustion of woods in a campfire say suppose. The burning wood is an open system because the heat and the mass are not bonded by any wall and the matter can be easily transferred to the surrounding.

is thermal equilibrium a system
Bonfire, Image Credit: Pixabay

The air gushing through the campfire grasps the heat energy and transfers it to the surrounding region thus warming the air in the surrounding region. This heat generated is spread around the campfire by convection. The system tries to gain the thermal equilibrium state by emitting the heat energy generated by the combustion of wood in the surrounding.

How to find the thermal equilibrium of a system?

To find the thermal equilibrium of a system we need to consider the rate of flow of heat, the mass, and the specific heat of a matter.

The system attaining the thermal equilibrium state is only by the flow of the heat energy that is present with it. Hence, the rate of flow of heat determines the time required to bring the system to its thermal equilibrium state.

Eventually, when there is no exchange of heat and the flow stops, the system is said to be in an equilibrium state.

Suppose we have two closed containers, one is hot and the other one is cold in temperature. Both the containers are kept in close contact with each other. The heat flow occurs from the hot container to the cold container. Hence, the heat energy lost from the hot container will be equal to the heat energy gained by the cold container. That is,


The heat energy is given by the formula as:


Here, Q is heat energy,

c is a specific heat capacity, and

m is a mass,

ΔT is a change in temperature due to the flow of heat energy from one system to another.

If the temperature of a system is decreased than its initial temperature, then the rate of heat energy will be negative indicating the loss of heat. While, if the final temperature of the system is more than its initial then it signifies the heat energy gained by the system.

What is the thermal equilibrium temperature of 20 grams of Al foil that is heated at a temperature of 70 0C and kept in a beaker containing 50 grams of water at room temperature?

Given: The mass of an aluminum foil is, m= 20 grams.

The mass of water in a beaker is, M= 50 grams.

The temperature of aluminum foil is, T1=700C

The temperature of a water is, T2=270C

The specific heat capacity of water is, cw=1 Cal/g0c

The specific heat capacity of aluminum is,

The heat gained by the water will be equal to the heat lost by the aluminum foil.



Substituting the values in this expression, we get:

Hence, the temperature at which the aluminum foil and water will be in a thermal equilibrium state is 30.40C.


A thermal equilibrium of a system is a state at which the temperature of a system matches the temperature of a system. This temperature is called thermal equilibrium temperature. At this temperature, there is no heat flow from the system to the surrounding.


Hi, I’m Akshita Mapari. I have done M.Sc. in Physics. I have worked on projects like Numerical modeling of winds and waves during cyclone, Physics of toys and mechanized thrill machines in amusement park based on Classical Mechanics. I have pursued a course on Arduino and have accomplished some mini projects on Arduino UNO. I always like to explore new zones in the field of science. I personally believe that learning is more enthusiastic when learnt with creativity. Apart from this, I like to read, travel, strumming on guitar, identifying rocks and strata, photography and playing chess. Connect me on LinkedIn -

Recent Posts