Zeroth Law of Thermodynamics

The Zeroth Law of Thermodynamics can be stated in several ways, but the simplest is as follows: systems in thermal equilibrium exist at the same temperature.

If a system does not transmit heat despite being in a position to do so due to other causes, it is said to be in thermal equilibrium. Food left in the refrigerator overnight, for example, has reached thermal equilibrium with the air in the refrigerator: heat no longer moves from one source (the food) to the other (the air) or back.

Temperature is something worth monitoring, according to the Zeroth Law of Thermodynamics, because it shows whether heat will transfer between objects. Regardless of how the items interact, this will be true. Even if two things do not come into contact, heat can nevertheless move between them via radiation (as from a heat lamp). However, if the systems are in thermal equilibrium, no heat flow will occur, according to the Zeroth Law of Thermodynamics.

There are several formal methods to express the Zeroth Law of Thermodynamics, which is typically written as follows:

Consider three systems: A, B, and C. If A and C are in thermal equilibrium, and A and B are in thermal equilibrium, then B and C are too.

Example:

The temperature of a person’s body is measured using a thermometer when he or she has a fever. When a thermometer is kept in close proximity to a person, heat from the person’s body transfers to the mercury in the thermometer, increasing the volume of mercury. The rise in the volume of mercury ends when the temperature of the body and that of the mercury in the thermometer are equal, and the scale on the thermometer is measured, which reveals the value of fever on the person’s body.

 Zeroth Law of Thermodynamics’ Importance: 

Mathematical theories frequently require an equivalence relation, which is a technique of determining whether two entities are the same or not. Because it allows for the mathematical concept of temperature and the presence of physical thermometers, the zeroth law is known as the equivalence relation of thermodynamics.

How Energy and Temperature can be distinguished:

The distinction between energy and temperature is an important notion. Knowing how much energy two separate items possess is insufficient to predict which way heat will travel when they come into contact. The direction of heat flow is determined by the relative temperatures of the two systems.

But how can you tell if it’s hot or cold? 

A thermometer is an object that, depending on its temperature, exhibits known and calibrated properties. When mercury heats up, for example, it expands in volume in a predictable way.

The temperature of an object can be measured by putting the thermometer in thermal equilibrium with it and then measuring its attributes, such as how much the mercury has expanded.

When attempting to compare the temperatures of two things, the zeroth law comes into play. When a thermometer is submerged in liquid A, it achieves thermal equilibrium and reads a specific temperature.

The Relationship Between Thermodynamics’ Zeroth Law and Temperature:

A body’s temperature is a thermodynamic variable that determines a surface’s degree of hotness or coldness.

A hot object has a higher temperature than a cold object, which has a lower temperature. We know that thermal equilibrium is reached when two bodies in touch reach a constant temperature since temperature is a relative variable.

Heat is transferred from a hot thing to a colder item, or, to put it another way, hot objects lose heat energy while cold objects acquire it.

When the exchange of heat energy between two bodies in thermal contact stops, the bodies reach a constant temperature and thus attain thermal equilibrium.

Thermodynamics’ Zeroth Law  Applications:

1. When a cup of hot tea is left open, it cools down. The heat of the tea is lost to the environment. As described by the zeroth law of thermodynamics, it eventually achieves thermal equilibrium when the temperature of the surroundings equals the temperature of the tea.
2. The zeroth law of thermodynamics governs the operation of a mercury thermometer. When the thermometer is put over a hot surface, the mercury in the tube expands, and the height of the mercury level rises, indicating a higher temperature.
3. A chilly glass of water cools down over time.
4. When fruits and vegetables are kept in the refrigerator for an extended period of time, they reach the refrigerator’s temperature.

Conclusion:

When two bodies are in thermal equilibrium with a third body, the Zeroth Law of Thermodynamics states that the two bodies are likewise in thermal equilibrium with each other. We can explain the concept of temperature with the help of the zeroth law of thermodynamics. This law states that temperature is important to measure since it determines whether or not heat exchange occurs between items.

 That is, if systems A and B are in thermal equilibrium with system C independently, then TA=TC and TB=TC, or TA=TB.

Where  TA,TB, and TC are the temperatures of systems A,B, and C, respectively.