How is Thermal Equilibrium Important in Physics?

The movement of energy from a high to a low temperature is known as heat. The system (or combination of systems) is in thermal equilibrium when these temperatures balance out, halting heat flow. Neither matter nor heat is going into or out of the system under such conditions. 

Thermal equilibrium is defined by the zeroth law of thermodynamics in Physics. This rule describes how we can bring two different systems at the equivalent temperature. When molten rock rises from a volcano, it releases heat into the atmosphere until both the rock and the atmosphere reach equilibrium. 

Thermal equilibrium allows temperature specification in rock and atmosphere despite the vast differences between the two systems (rock and air).

Over time, all systems tend to reach thermal equilibrium—though some take much longer than others. Understanding that cooperating entities would grow to the same temperature brings up a whole new universe of scientific possibilities. 

The specific heat capacity of a substance, for example, can be determined by immersing it in water and monitoring the temperature over time.

Why is Thermal Equilibrium Important?

Thermodynamics’ applications are dense both at the macro and micro levels. 

For the Global average temperature to stay constant, thermal equilibrium is essential. Solar energy on Earth must be balanced, which means that it must reflect the same amount of heat that it absorbs. By slowing heat transit from World to space, the greenhouse effect causes the Earth to become hotter.

The natural greenhouse effect is required for the Earth’s temperature to be habitable for people and other animals, and without it, this planet would be way too chilly.  However, as carbon dioxide, methane, and nitrogen dioxide levels climb in the atmosphere, the greenhouse effect becomes more assertive. 

It forces the Earth to release somewhat less heat than is absorbed in its energy exchanges. This small out of balance leads to a warming climate, challenging the survival of life on Earth. 

Thermal Equilibrium Equation

Before understanding the thermal equilibrium calculation, let us briefly discuss the thermal equilibrium equation. 

For achieving thermodynamic equilibrium, heat must transfer from the warmer to the cooler item. If no heat moves between two objects connected by a heat-permeable pathway causing no fluctuation in either temperature, they are in thermal equilibrium. 

The above rule is known as the zeroth law of thermodynamics. If the temperature within a system is geographically and temporally uniform, we can consider it in thermal equilibrium amongst itself.

Thermally isolated systems are thermodynamic systems that do not exchange mass or heat energy with their environment. The law of energy conservation asserts that an isolated system’s total energy remains unchanged in a given frame of reference — it is said to be maintained over the duration.

The first law of thermodynamics states that the amount of energy obtained by a system during an interaction with its surroundings must be equal to the amount of energy lost by the surroundings. 

We can argue that in a thermally isolated system, the amount of energy gained by one object must be exactly equal to the amount of energy lost by another during an interaction between objects within the system. 

Example of Basic Thermal Calculations

Here is a simple illustration of thermal equilibrium calculation on cooling a hot object by submerging it in water. The second law of thermodynamics states that the hot object and the water will reach thermal equilibrium with time.  Assume that the tank is indoors, at a constant temperature of 20 degrees Celsius, as established by our system. It is filled with 100L of water. 

We dip a 10 kg cast iron object with a specific heat of 0.46 joule/gr*Celsius and a temperature of 500 degrees Celsius in water. What will the temperature be in the end?

We assume that the heat energy lost from the cast iron object will be the same as the heat energy received by the water in the process. We can make this assumption using the calculation presented in the “specific heat” portion.

So we have Qci = Qw => cmciΔΤci = cmwΔΤw => 0.46 x 10000 x(500-Tfinal) = 4.186x100000x(Tfinal-20) => Tfinal = 25.2 degrees Celsius. 

The water in the tank and the cast iron object will reach this temperature.

Conclusion

That’s a wrap on why thermal equilibrium is important in physics!

It is basic arithmetic to calculate the equilibrium temperature, a thermodynamic limit. Predicting how near a system will approach equilibrium is a more difficult heat transfer problem. 

Conduction is dependent on the thermal conductivity and size of the delivered product particles. In contrast, convection depends on turbulence and the difference in air and product velocity. Conduction and convection are the two components of heat transmission.