laws of thermodynamics

Thermodynamics

Thermodynamics can be defined as the science of energy.

The name thermodynamics stems from the Greek words therme (heat) and

dynamis (power), which is most descriptive of the early efforts to convert

heat into power. Today the same name is broadly interpreted to include all

aspects of energy and energy transformations including power generation,

refrigeration, and relationships among the properties of matter.

There are Four laws of thermodynamics-

Zeroth law of thermodynamics-

The zeroth law of thermodynamics states that if two systems, A and B, are in thermal equilibrium with a third system, C, then A and B are in thermal equilibrium with each other.

We can understand easily with this image-

The first law of thermodynamics- 

This law is known as Law of Conservation of Energy, states that energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another. For example, When we throw a ball in the sky we provide it K.E. But when the ball reaches the topmost point it's whole K.E. converted into P.E. so, here whole energy is conserved.

The change in the energy content of a body or any other
the system is equal to the difference between the energy input and the energy
output and the energy balance is expressed as

Ein-Eout = ΔE

The second law of thermodynamics-

The second law of thermodynamics asserts that energy has quality as well as quantity, and actual processes occur in the direction of decreasing the quality of energy.

The second law of thermodynamics state that the entropy of an isolated system always increases. Isolated systems spontaneously evolve towards thermal equilibrium—the state of maximum entropy of the system. 

In simple words- the entropy of the universe (the ultimate isolated system) only increases and never decreases.

For example, a cup of hot coffee left on a table eventually cools, but a cup of cool coffee in the same room never gets hot by itself

Heat Engines

Second Law of Thermodynamics: It is impossible to extract an amount of heat Q_H from a hot reservoir and use it all to do work.

Kelvin plank statement-

It is impossible to construct an engine which operates in a cycle and produce work output by extracting heat with a single reservoir. this device is known as perpetual motion machine 2 (PPM2)

Clausis Statement-

The Clausius Statement: It is impossible to construct a device which operates on a cycle and produces no other effect than the transfer of heat from a cooler body to a hotter body without any external work

it gives the concept of refrigerator and pump

The third law of thermodynamics

The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero.

         The entropy of a pure perfect crystal is zero (0) at zero Kelvin (0° K)." Entropy is a property of matter and energy discussed by the Second Law of Thermodynamics. The Third Law of Thermodynamics means that as the temperature of a system approaches absolute zero, its entropy approaches a constant (for pure perfect crystals, this constant is zero). A pure perfect crystal is one in which every molecule is identical, and the molecular alignment is perfectly even throughout the substance. For non-pure crystals, or those with less-than-perfect alignment, there will be some energy associated with the imperfections, so the entropy cannot become zero.

Watch it in powerpoint