Thermal equilibrium


The ideas regarding the origin and the nature of the term heat , have been varying during the last centuries. The thermal equilibrium is focused on understanding the behavior with the physical systems with respect to the ideas of the heat and temperature . The field of thermal physics is remarkable and is applied to a great extent to all knowledge systems of thermal physics in order to better understand physics. Thermal equilibrium is a state in which equalize the temperaturesthat have two bodies that initially haddifferent temperatures , suspending the heat flow to achieve a proper balance .


What is thermal equilibrium?

Thermal equilibrium is a process that includes the fact that two systems that are in contact with each other have a uniform temperature , it is a state to which the systems tend when they come into contact with each other.

  • What is thermal equilibrium?
  • What is it for
  • What does the principle of thermal equilibrium say
  • Explanation
  • Calculation
  • Experiments
  • Examples of thermal equilibrium

What is thermal equilibrium?

Thermal equilibrium consists of regulating the temperatures of two bodies that are at different temperatures, where the body that has a higher temperature gives a part of its energy to the body that has a lower temperature until they are equal. It is a state in which the temperatures of the bodies that at the beginning had different temperatures are matched . When this happens, the heat flow between the bodies is suspended, thus reaching the correct balance .


What is it for

Thermal equilibrium helps us to understand some aspects of the operation of the different processes that occur in nature , to understand how energy losses occur in machines and to develop better efficiency in machines.

What does the principle of thermal equilibrium say

So theoretical , the principle of thermal equilibrium is a fundamental aspect of the Act Zero , which tells us that if two systems are separated are at a moment in thermal equilibrium with a third system, the first in equilibrium thermal with each other. It is a very important principle that is applied in thermodynamics , which is the branch of physics that is responsible for describing the different states of equilibrium that occur at a level .


When a body is hot it is easy to recognize, but it is sometimes difficult to explain the reason for this happening or to establish the type of process inside the body for this situation to arise. When a body is heated, the particles within it begin to move rapidly ; the hotter the object, the faster its particles will have.

Assuming this movement of particles, it is necessary to know what happens when two groups of particles come into contact. When the two systems have particles moving at different speeds , those that are moving at a lower speed are accelerated , and those that are moving at a higher speed are slowed down ; in other words, they find a balance . The process must take into account the processes of the world that we experience through the senses . In the case of two objects, the hot one will pass its heat to the colder one until they reach an equilibrium that leads them to express the same temperature.


The equation that shows us the quantification of the amount of heat that is exchanged in the transfers between the bodies is the following:

Q = M * C * ΔT


  • Q represents the amount of heat which is expressed in calories
  • M represents the mass of the body under study
  • C represents the specific heat that the body has
  • DT represents the difference of temperature .

There is also another important equation to get an idea of ​​thermal equilibrium. This equation tries to express the temperature that the system will have when it is unified . When a system of N1 particles, which is at temperature T1, comes into contact with another system of N2, the equilibrium temperature is obtained by the formula:

(N1 * T1 + N2 * T2) / (N1 + N2)

When both subsystems have the same amount of particles , the temperature of equilibrium decreases to an average between the two initial temperatures .



  • Measure the ambient temperature .
  • Place a can in a glass of water and measure the temperature of the water and the sand.
  • We repeat the steps every three minutes, and record the data in a table of values.
  • We graph t = f (time) for water and sand.

After some time, the following final temperatures of the water, sand and the environment are recorded:

Water temperature = 15 ° C t sand = 15 ° C t ambient = 15 ° C


As time passes it can be seen that:

  • The water temperature decreases .
  • The temperature of the sand increases .
  • The two temperatures are roughly equal to 50 ° C.
  • When temperatures equalize, they decrease .

Examples of thermal equilibrium

Some examples of thermal equilibrium are as follows:

When it has done measuring the temperature of the body by a thermometer . The duration that the thermometer must have when it is in contact with the body to correctly quantify the degrees of temperature is due to the time it takes to reach thermal equilibrium .

The products are sold so naturally were probably in a refrigerator . However, after some time that they have been out of the refrigerator and that they have been in contact with the natural environment , they reached thermal equilibrium with it.

When a person gets out of the shower , they may experience a cold , this because the body had entered into equilibrium with the hot water , and for this reason it must come into balance with the environment.

When cold water is added at a rate that contains hot water, where equilibrium is reached very quickly at a temperature colder than the original temperature.

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