Question

What is the first three laws of thermodynamics?

Answer 1

Laws of thermodynamics:

There are four laws of thermodynamics, and they are as follows:

1. First Law of Thermodynamics
2. Second Law of Thermodynamics
3. Third Law of Thermodynamics
4. Zeroth law of thermodynamics

First Law of Thermodynamics: -

1. It states that, “Energy can neither be created not destroyed. It can only be converted from one form to another”.
2. It is also called the law of conservation of energy.
3. Mass crossing the control boundary, external work, or heat transfer across the barrier are all examples of energy transfer for any system.
4. These result in a change in the control volume's energy reserves.

$∆U=q+W$

Where, $∆U$ is change in internal energy of the system, $q$ is algebraic sum of heat transfer between system and surroundings, $W$ is work interaction of the system with its surroundings.

Second Law of Thermodynamics:

1. It states that, “Heat never flows from a colder body to a hotter body, except when external energy is applied”.
2. In some interpretations, the concept of entropy is established as a physical characteristic of a thermodynamic system by the second law of thermodynamics.
3. It offers necessary criteria for spontaneous processes and can be used to determine whether processes are prohibited even when they comply with the first rule of thermodynamics' requirement for energy conservation.
4. If $S$ is the entropy of a system, $Q$ is the heat added to the system and $T$ is the absolute temperature of the system, the
   $∆S=\frac{Q}{T}$
5. Also, $S_{\text{universe}}>0$

Third Law of Thermodynamics:

1. It states that, “the entropy of a system approaches a constant value as the temperature approaches absolute zero”.
2. The third law of thermodynamics focuses on how systems behave as the temperature gets closer to zero degrees.
3. It relates heat and entropy at this very low temperature for crystals.
4. The entropy of a flawless crystal is zero when its temperature is equal to absolute zero ($0K$), according to the third law of thermodynamics.
5. Mathematically,
   $S=k_B\log W$
   where $k_B$ is Boltzmann's constant, and $W$ is the total number of microstates that are consistent with the system’s macroscopic configuration.