Absolute Zero Temperature: Ideal Temperature: Coldest Possible Temperature

When German chemist WALTHER HERMAAN NERNST studied about the second law of thermodynamics, his mind was completely disturbed. He studied that the entropy of the universe keeps on increasing for all the processes occurring on its own. He thought that, what should be done so that the entropy of the universe will not increase and it will remain constant?

Then he studied everything about entropy. After a lot of studying and research work, he discovered the "Third Law Of Thermodynamics". In that, he used the concepts of "Absolute Zero Temperature" to limit the value of entropy to a pure perfect crystalline substance. He states the third law as "The entropy of a perfect crystal of a pure substance approaches zero as the temperature approaches zero". 

Generally, entropy increases with increase in system temperature and decreases with decrease in system temperature. At Absolute Zero Temperature (0 Kelvin temperature), all modes of motion stop (no translational, no rotational, no vibrational motion).

Let Us Now Understand About Absolute Zero Temperature

You know very well that higher the temperature of the body, higher the molecular vibration inside the body. And if the temperature of the body is less, then the molecular vibration is also less. If we keep on reducing the temperature of the body, then all the molecules and atoms will stop the motion and they will be completely freezed.

As you can see in the above images, as the temperature keeps on decreasing, the motion of molecules is also decreasing. In the last part, you can see that all the molecules are freezed and they are not moving. Thus, the temperature at which the kinetic energy of all the molecules becomes zero is called Absolute Zero Temperature. Even gases like hydrogen, helium, oxygen get freezed up and become solids at this temperature.

At zero Kelvin temperature, average kinetic energy of molecules becomes zero and molecules motion stop.

DEFINITION OF ABSOLUTE ZERO

"Absolute zero is the lowest (coldest) possible temperature ever where nothing could be colder and no heat energy remains in a substance. It is a theoretical temperature and is measured on the Kelvin scale". It is the lowest temperature that can be attained without breaking the laws of physics. Scientists know that such temperature exist. But they have never been able to achieve this lowest temperature even by using many scientific techniques and freezers. Scientists have achieved temperature somewhat close to absolute zero in a laboratory, but not exactly Zero Kelvin. Thus, Absolute zero is unattainable in reality. Therefore, it can only be approached.

By international agreement, Absolute zero temperature is represented as:

1. 0 Kelvin on Kelvin Scale
2. -273.15 °C on Celsius scale
3. -459.67 °F on Fahrenheit Scale

ABSOLUTE ENTROPY

"Absolute Entropy of a pure substance at a given temperature,T will be the sum of the total entropy obtained by heating it from absolute zero temperature to a particular temperature,T". It is based on the reference point of zero entropy at zero kelvin temperature. The sign of entropy of any substance is always positive at any temperature above absolute zero temperature. The absolute Entropy;

In practice (as shown above), chemists determine the absolute entropy of a substance by measuring the molar heat capacity (Cp) as a function of temperature and then plotting the quantity Cp/T versus T. The area under the curve between 0 K and any temperature T is the absolute entropy of the substance at T.

Points To Remember

☛ Temperature does not have a negative value in the Kelvin scale and has the lowest possible value of zero. 

☛ Absolute zero is so so soooooo…… much colder than whatever you might have experienced in your life. 

☛ At absolute zero temperature, the thermodynamic system must be in a state with minimum thermal energy and all molecular motion within the system will stop. And also no heat energy within the system at this temperature.

☛ The atoms and molecules of any substance will not be able to move, vibrate or oscillate inside the substance at this temperature. 

☛ Absolute zero is the point at which fundamental particles of nature have minimum vibrational motion, with only quantum mechanical, zero-point energy-induced particles retaining motion.

FAQs

Does anything exists at an absolute zero temperature???

yes,I think so……

What is the statement of third law of thermodynamics based on Absolute Zero Temperature??

The statement of third law of thermodynamics states that the entropy of a pure perfectly crystalline substance vanishes at absolute zero temperature. At temperatures near Zero Kelvin (−273.15 °C; −459.67 °F), nearly all molecular motion ceases and ΔS = 0 where S is entropy.

Can entropy be zero practically????

Theoretically entropy can (very loosely there is much debate) be zero; however practically one cannot achieve this because to have entropy at 0,  the temperature reached must be 0 kelvin (Absolute zero); and that can't be reached.

Why the absolute zero temperature is not attainable in practice???

One version of third law states that-"It would require an infinite number of steps to reach absolute zero, which means you will never get there. If you get the absolute zero temperature, it would violate the second law of thermodynamics because if you had a heat sink at absolute zero, then you could build a machine that was 100% efficient". Therefore, it can only be approached.

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