Laws of Thermodynamics

The Thermodynamics is the Branch of Physics that is in charge of determine and measure Energy Transfer phenomena, encompassing Heat and Mechanical Work.

Energy

One of the most fundamental manifestations of nature is the energy that accompanies all changes and transformations. Thus, phenomena as diverse as the fall of a stone, the movement of a billiard ball, the combustion of coal, or the growth of and reactions of the complex mechanisms of living beings, all comprise some absorption, emission and redistribution of the Energy.

The most common form in which Energy appears and towards which others tend, is the Hot. Next to him occurs Mechanical energy in the movement of any mechanism.

Electrical Energy when a current heats a conductor or is capable of performing mechanical or chemical work. Radiant energy inherent to visible light and radiation in general; and finally the Chemical Energy stored in all substances, which is revealed when they carry out a transformation.

As different and diverse as at first glance they may be supposed, however, they are intimately linked to each other, and under certain conditions a conversion takes place from one to the other.

It is a matter of thermodynamics study such interrelationships that take place in systems, and their laws, which are applicable to all natural phenomena, are rigorously fulfilled since They are based on the behavior of macroscopic systems, that is, with a large number of molecules instead of microscopic ones that comprise a reduced number of they.

To the Systems where the Laws of Thermodynamics, they are called Thermodynamic Systems.

Thermodynamics does not consider the transformation time. Your interest focuses on the Initial and Final states of a System without showing any curiosity about the speed with which such change occurs.

The Energy of a given System is Kinetic, Potential or both at the same time. The Kinetic energy it is due to its movementwell be molecular or of the body as a whole.

On the other hand, Potential is that kind of energy that a system possesses by virtue of its position, that is, by its structure or configuration with respect to other bodies.

The total Energy content of any system is the sum of the previous ones, and although its absolute value can be calculated taking into account the famous Einstein relation E = mC², where E is Energy, m is mass, and C is the speed of Light, this fact is of little use in ordinary thermodynamic considerations.

The reason is that the Energies involved are so great that any change in them as a result of physical or chemical processes is negligible.

Thus the mass changes resulting from those transfers are imponderable, so the Thermodynamics prefers to deal with such Energy differences that are measurable and are expressed in various systems of units.

For example, the unit of the cgs System of Mechanical, Electrical, or Thermal Energy is the Erg. That of the International System of Units is the Joule or July; that of the English System is the Calorie.

The Thermodynamics is governed by four Laws, based on the Zero Law.

Zero law of thermodynamics

It is the simplest and most fundamental of the four, and it is basically a premise that says:

"If a body A is in Thermal Equilibrium with a body B, and body C is in Equilibrium with B, then A and C are in Equilibrium."

First Law of Thermodynamics

The First Law of Thermodynamics establishes the Conservation of Energy with the premise that it says:

"Energy is neither created nor destroyed, it only transforms."

This law is formulated by saying that for a given quantity of a form of Energy that disappears, another form of it will appear in an amount equal to the quantity that has disappeared.

It is considered the destination of a certain amount of heat (Q) added to the system. This quantity will give rise to a increase in internal energy (ΔE) and it will also effect certain external work (W) as a consequence of said heat absorption.

It is held by the First Law:

ΔE + W = Q

Although the First Law of Thermodynamics establishes the relationship between absorbed heat and work performed by a system, does not indicate any restriction on the Source of this heat or in the direction of its flow.

According to the First Law, nothing prevents that without external help we extract heat from the ice to heat the water, the temperature of the former being lower than that of the latter.

But it is known that The heat flow has the only direction from the highest to the lowest temperature.

Second Law of Thermodynamics

The Second Law of Thermodynamics addresses the inconsistencies of the First Law, and carries the following premise:

"Heat is not transformed into Work without producing permanent changes either in the systems included or in their vicinity."

Entropy is the physical quantity that defines the Second Law of Thermodynamics, and it depends on the Initial and Final states:

ΔS = S₂ - S₁

The Entropy of the whole process is also given by:

ΔS = q_r/ T

Being q_r the heat of a reversible isothermal process and T the Constant Temperature.

Third Law of Thermodynamics

This Law deals with the Entropy of pure Crystalline substances at Absolute Zero Temperature, and its premise is:

"The entropy of all Pure Crystalline Solids must be considered zero at Absolute Zero Temperature."

This is valid because experimental evidence and theoretical arguments show that the entropy of supercooled solutions or liquids is not zero at 0K.

Examples of Applications of Thermodynamics

Domestic refrigerators

Ice Factories

Internal combustion engines

Thermal containers for hot drinks

Pressure Cookers

Kettles

Railways powered by coal burning

Metal smelting furnaces

The Human Body in Search of Homeostasis

Clothes worn in winter keep the body warm