## Zeroth Law of Thermodynamics

Zeroth Law of Thermodynamics: Zeroth's law of thermodynamics is one of the Four Laws of thermodynamics. Zeroth's Law of Thermodynamics states that “When two bodies are in thermal equilibrium with the third body the two bodies are also in thermal equilibrium with each other, hence all three bodies are in equilibrium with each other". This law was discovered by Ralph H. Fowler in the year the 1930s, after the discovery of the first, second, and third laws of thermodynamics which had achieved widespread acceptance at that time.

## Explanation: Zeroth Law of Thermodynamics

Let us suppose two systems 'A' and ‘B’, are separated by a wall that does not allow any exchange of heat or energy between them. Such a type of wall is called an insulating wall or adiabatic wall. The third system 'C' is separated from systems A and B by a wall which is conducting which is called a diathermic wall or Conducting wall. The systems that are connected by the conducting or diathermic wall can exchange heat or energy between both systems, and hence they are said to be in thermal equilibrium. Similarly, energy can be exchanged between the other systems, so both are also said to be in thermal equilibrium. In other words, both systems are said to be in thermal equilibrium with the third system separately. Now, there will be no transfer of energy when the adiabatic wall is removed from the two systems. This is what zero law states. We can say-

The temperature of A = Temperature of C,

The temperature of B = Temperature of C,

Therefore, The temperature of A = Temperature of B

## Term Relating to Zeroth Law of Thermodynamics

The common term relating to the zeroth law of thermodynamics is-

Thermal Equilibrium: The state of the system is said to be in thermal equilibrium when the state of the system does not change over time. Two objects are not in thermal equilibrium when the state of the system changes with time. For instance, a colder object touches a hotter object—like ice that has been dropped in a hot cup of coffee. After some time, the ice (later water) and the coffee will reach a certain temperature where there will not be any increase or decrease in temperature. Therefore, the temperature remains constant. Such a condition is referred to as thermal equilibrium.

## Application of Zeroth Law of Thermodynamics

The zeroth law of thermodynamics is applied in everyday situations.

• The thermometer is a well-known example of the zeroth law.
• If you take a glass of ice water and a glass of hot water and place them on the kitchen countertop for some time, thus the time will come when eventually it will attain thermal equilibrium with the room. Therefore, the temperature of all three becomes constant.
• If you place a package of milk in your freezer and leave it overnight, you assume that the milk has reached the same temperature as the freezer and the other items in the freezer.
Zeroth Law of Thermodynamics- FAQs

Ans. Zeroth's Law of Thermodynamics states that “When two bodies are in thermal equilibrium with the third body the two bodies are also in thermal equilibrium with each other, hence all three bodies are in equilibrium with each other".

Ans. The state of the system is said to be in thermal equilibrium when the state of the system does not change over time.

Ans. A thermodynamic system is a system in which a body of matter is confined within the walls that separates the system from the surrounding. Thermodynamic systems can be three types: Isolated thermodynamics system, Closed thermodynamics System, Open thermodynamics System.

Ans. It includes everything other than the system. The universe together comprises both systems and surroundings.

Ans. The zeroth law of thermodynamics is applied in everyday situations are- The thermometer is a well-known example of the zeroth law, If you take a glass of ice water and a glass of hot water and place them on the kitchen countertop for some time, thus the time will come when eventually it will attain thermal equilibrium with the room. Therefore, the temperature of all three becomes constant. If you place a package of milk in your freezer and leave it overnight, you assume that the milk has reached the same temperature as the freezer and the other items in the freezer.