Laws of Thermodynamics

the nature has not yet given the mankind permission to create energy on its own. This is what the First Law of Thermodynamics says. It says that energy can neither be created nor it can be destroyed though it can be converted from one form to the other. The field of study of thermodynamics is based on three laws of thermodynamics and Zeroth’s law.


The Second Law of Thermodynamics states that heat energy can be transferred only from body at high temperature to the body at lower temperature. Since heat is directly proportional to temperature, this law can also be understood as: heat energy can flow only from high energy reservoir to low energy reservoir. If you want to move the heat energy from low temperature reservoir to high temperature reservoir, external work has to be performed. In refrigeration and air-conditioning system, heat moves from low temperature to high temperature reservoir, hence they need power (electricity) to work.


The Third Law of Thermodynamics is lesser known of all the laws. It refers to absolute zero, the zero temperature on Kelvin temperature measurement scale. Absolute zero on Kelvin scale is different from zero degree Celsius (freezing point of water). Absolute zero = (-273) degree Celsius. So third law of thermodynamics says that entropy of the body at absolute zero is zero and it can never be negative.

Then finally we have Zeroth’s Law of Thermodynamics, which states that if two bodies are in thermal equilibrium with third body, then they are in thermal equilibrium with each other. For example, if temperature of body A is equal to temperature of body C and temperature of body B is also equal to temperature of body C, then temperature of body A is equal to that of B.

The laws of thermodynamics seem very basic and quite logical, but the deep study of this subject has led to innovations of most of the modern machines and equipments. Most of the equipments studied under Mechanical Engineering are the outcomes of various laws of thermodynamics; hence thermodynamics is an important subject area of this branch of Engineering. Some of the popular innovations which are outcome of applications of various laws of thermodynamics are automobiles, refrigerators, air-conditioners, HVAC, all type of power plants, airplanes etc. The study of thermodynamics has brought a sort of revolution in the lives of mankind. You can imagine your life without electricity, automobiles, or airplanes

Development of the Laws of Thermodynamics

The study of heat as a distinct form of energy began in approximately 1798 when Sir Benjamin Thompson (also known as Count Rumford), a British military engineer, noticed that heat could be generated in proportion to the amount of work done ... a fundamental concept which would ultimately become a consequence of the first law of thermodynamics.
French physicist Sadi Carnot first formulated a basic principle of thermodynamics in 1824. The principles which Carnot used to define his Carnot cycle heat engine would ultimately translate into the second law of thermodynamics by the German physicist Rudolf Clausius, who is also frequently credited with the formulation of the first law of thermodynamics.

Part of the reason for the rapid development of thermodynamics in the nineteenth century was the need to develop efficient steam engines during the industrial revolution.

Kinetic Theory & the Laws of Thermodynamics

The laws of thermodynamics do not particularly concern themselves with the specific how and why of heat transfer, which makes sense for laws that were formulated before atomic theory was fully adopted. They deal with the sum total of energy and heat transitions within a system, and do not take into account the specific nature of heat transference on the atomic or molecular level.