Laws of thermodynamics: Zeroth, First, Second, and Third laws

Zeroth Law of Thermodynamics

1. The Zeroth Law of Thermodynamics defines the concept of thermal equilibrium.
2. If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other.
3. This law provides the foundation for the definition of temperature.
4. Thermometers work based on the Zeroth Law.

First Law of Thermodynamics

1. The First Law of Thermodynamics is a statement of the conservation of energy.
2. It states: ΔU = Q − W, where:
   • ΔU is the change in internal energy.
   • Q is the heat added to the system.
   • W is the work done by the system.
3. The law implies that energy cannot be created or destroyed, only transformed from one form to another.
4. The First Law explains processes like heating, cooling, and expansion of gases.
5. In an isolated system, the total energy remains constant.
6. The law forms the basis for energy management in systems like engines and refrigerators.

Second Law of Thermodynamics

1. The Second Law of Thermodynamics introduces the concept of entropy.
2. It states that in any natural process, the total entropy of a system and its surroundings always increases.
3. Heat cannot spontaneously flow from a colder body to a hotter body without external work.
4. This law explains the irreversibility of natural processes.
5. The efficiency of a heat engine is limited by the Carnot cycle.
6. The formula for efficiency is: η = 1 - (T₂/T₁), where:
   • T₁ is the temperature of the hot reservoir.
   • T₂ is the temperature of the cold reservoir.
7. The Clausius statement and Kelvin-Planck statement are two equivalent forms of the Second Law.
8. Entropy, a measure of disorder, tends to increase in isolated systems.
9. The law governs the direction of processes like heat flow and chemical reactions.

Third Law of Thermodynamics

1. The Third Law of Thermodynamics states that the entropy of a perfect crystal at absolute zero is exactly zero.
2. As the temperature approaches absolute zero (0 K), the entropy of a system approaches a constant value.
3. This law implies that it is impossible to reach absolute zero in a finite number of steps.
4. The Third Law is significant for understanding low-temperature phenomena.
5. Applications include the study of superconductivity and cryogenics.

Applications of the Laws of Thermodynamics

1. These laws are fundamental to the design of engines, refrigerators, and air conditioning systems.
2. The Zeroth Law is essential for temperature measurement.
3. The First Law is used to calculate energy changes in chemical reactions and phase changes.
4. The Second Law is critical for analyzing the efficiency of heat engines and power plants.
5. The Third Law is crucial for research in low-temperature physics and thermodynamic processes.
6. These laws govern the behavior of gases, liquids, and solids in thermodynamic systems.
7. The principles are applied in understanding the Earth's atmosphere and weather systems.
8. Advanced technologies like fuel cells and heat pumps rely on these thermodynamic principles.
9. The laws provide the foundation for energy conversion and utilization in all mechanical systems.