History of Thermodynamics

The history of thermodynamics is a fundamental strand in the history of physics, chemistry and the history of science in general. Many people had a hand in forming the science of thermodynamics, but the foremost were Nicolas Carnot and Lord Kelvin.

Nicolas Carnot in the History of Thermodynamics

Nicolas Carnot (1796-1832)

Nicolas Léonard Sadi Carnot was a French military engineer and physicist, often described as the “father of thermodynamics“. In his only publication, the 1824 monograph Reflections on the Motive Power of Fire, Carnot gave the first successful theory of the maximum efficiency of heat engines. Carnot’s work attracted little attention during his lifetime, but it was later used by Rudolf Clausius and Lord Kelvin to formalize the second law of thermodynamics and define the concept of entropy.

lord kelvin and the History of Thermodynamics

Lord Kelvin (1824 – 1907)

William Thomson, 1st Baron Kelvin OM GCVO PC PRS FRSE  was an Irish mathematical physicist and engineer who was born in Belfast in 1824. At the University of Glasgow he did important work in the mathematical analysis of electricity and formulation of the first and second laws of thermodynamics, and did much to unify the emerging discipline of physics in its modern form.


the history of thermodynamics

The Carnot Cycle

In 1824, Nicolas Léonard Sadi Carnot proposed a model for a heat engine based on what has come to be known as the Carnot cycle. The cycle exploits the relationships among pressure, volume and temperature of gasses and how an input of energy can change form and do work outside the system.

Compressing a gas increases its temperature so it becomes hotter than its environment. Heat can then be removed from the hot  gas using a heat exchanger. Then, allowing it to expand causes it to cool. This is the basic principle behind heat pumps used for heating, air conditioning and refrigeration.

Conversely, heating a gas increases its pressure, causing it to expand. The expansive pressure can then be used to drive a piston, thus converting heat energy into kinetic energy. This is the basic principle behind heat engines.

The Four Laws of Thermodynamics

A brief explanation

The fundamental principles of thermodynamics were originally expressed in three laws. Later, it was determined that a more fundamental law had been neglected, apparently because it had seemed so obvious that it did not need to be stated explicitly. To form a complete set of rules, scientists decided this most fundamental law needed to be included. The problem, though, was that the first three laws had already been established and were well known by their assigned numbers. When faced with the prospect of renumbering the existing laws, which would cause considerable confusion, or placing the pre-eminent law at the end of the list, which would make no logical sense, a British physicist, Ralph H. Fowler, came up with an alternative that solved the dilemma: he called the new law the “Zeroth Law.”

The science of thermodynamics has been developed over centuries, and its principles apply to nearly every device ever invented. Its importance in modern technology cannot be overstated.

Article from livescience.com

The Zeroth Law
States that if two bodies are in thermal equilibrium with some third body, then they are also in equilibrium with each other. This establishes temperature as a fundamental and measurable property of matter.

The First Law
States that the total increase in the energy of a system is equal to the increase in thermal energy plus the work done on the system. This states that heat is a form of energy and is therefore subject to the principle of conservation.

The Second Law
States that heat energy cannot be transferred from a body at a lower temperature to a body at a higher temperature without the addition of energy. This is why it costs money to run an air conditioner.

The Third Law
States that the entropy of a pure crystal at absolute zero is zero. As explained above, entropy is sometimes called “waste energy,” i.e., energy that is unable to do work, and since there is no heat energy whatsoever at absolute zero, there can be no waste energy. Entropy is also a measure of the disorder in a system, and while a perfect crystal is by definition perfectly ordered, any positive value of temperature means there is motion within the crystal, which causes disorder. For these reasons, there can be no physical system with lower entropy, so entropy always has a positive value.