However, the word " heat " is a highly technical term in physics and thermodynamics, and is often confused with thermal energy.

The components of the word thermodynamics are derived from the Greek words θέρμη therme, meaning heat, and δύναμις dynamis, meaning power.

In thermodynamics, the term exothermic (" outside heating ") describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light ( e. g. a spark, flame, or explosion ), electricity ( e. g. a battery ), or sound ( e. g. burning hydrogen ).

In thermodynamics, the Joule – Thomson effect or Joule – Kelvin effect or Kelvin – Joule effect or Joule – Thomson expansion describes the temperature change of a gas or liquid when it is forced through a valve or porous plug while kept insulated so that no heat is exchanged with the environment.

This puts the time reversal symmetry of ( almost ) all known low-level fundamental physical processes at odds with any attempt to infer from them the second law of thermodynamics which describes the behaviour of macroscopic systems.

Classical thermodynamics describes the exchange of work and heat between systems.

It accounts for the occurrence of energy transfer by work in a process in which heat is also transferred ; the quantity, however, was considered before the relation between heat and work transfers was clarified by the invention of thermodynamics.

The enthalpy H ( S, p ) of homogeneous systems can be derived as a characteristic function of the entropy S and the pressure p as follows: we start from the first law of thermodynamics for closed systems for an infinitesimal process

Since, by the second law of thermodynamics, this is statistically improbable to the point of exclusion, the Carnot efficiency is a theoretical upper bound on the reliable efficiency of any process.

For thermodynamics and statistical thermodynamics to apply to a process in a body, it is necessary that the atomic mechanisms of the process fall into just two classes:

For a thermodynamic account of a process in terms of the entropies of small local regions, the definition of entropy should be such as to ensure that the second law of thermodynamics applies in each small local region.

# REDIRECT reversible process ( thermodynamics )

* 1824 – Sadi Carnot analyzes the efficiency of steam engines using caloric theory ; he develops the notion of a reversible process and, in postulating that no such thing exists in nature, lays the foundation for the second law of thermodynamics, and initiating the science of thermodynamics

For a given thermodynamics process, in order to specify the extent of a particular process, one of the properties ratios ( listed under the column labeled " known ratio ") must be specified ( either directly or indirectly ).

An artist depiction of two black hole s merging, a process in which the laws of thermodynamics are upheld.

* Isotherm in thermodynamics, a curve on a p-V diagram for an isothermal process

For this case, the first law of thermodynamics still holds, in the form that the internal energy is a function of state and the change of internal energy in a process is a function only of its initial and final states, as noted in the section below headed First law of thermodynamics for open systems.

The economic system, like all systems, is subject to the laws of thermodynamics, which define the limit at which the Earth can successfully process energy and wastes.

In 1843, Clapeyron further developed the idea of a reversible process, already suggested by Carnot and made a definitive statement of Carnot's principle, what is now known as the second law of thermodynamics.

* 1824-Sadi Carnot analyzes the efficiency of steam engines using caloric theory ; he develops the notion of a reversible process and, in postulating that no such thing exists in nature, lays the foundation for the second law of thermodynamics.

The law is an expression of the principle of conservation of energy, also expressed in the first law of thermodynamics, and that the enthalpy of a chemical process is independent of the path taken from the initial to the final state.

From the second law of thermodynamics, for a reversible process we may say that.

* Throttling process ( thermodynamics ), an isenthalpic process in thermodynamics

In the catalyzed elementary reaction, catalysts do not change the extent of a reaction: they have no effect on the chemical equilibrium of a reaction because the rate of both the forward and the reverse reaction are both affected ( see also thermodynamics ).

In basic chemistry scientists are typically interested in experiments conducted at atmospheric pressure, and for reaction energy calculations they care about the total energy in such conditions, and therefore typically need to use H. Furthermore the enthalpy is the working horse of engineering thermodynamics as we will see later.

This is studied in chemical thermodynamics, which sets limits on quantities like how far a reaction can proceed, or how much energy can be converted into work in a combustion engine and which provides links between properties like the thermal expansion coefficient and change of rate in entropy with pressure for a gas or a liquid.

Whether a reaction actually will go in the arbitrarily-selected forward direction or not depends on the amounts of the substances present at any given time, which determines the kinetics and thermodynamics, i. e., whether equilibrium lies to the right or the left.

Other major components include molecular dynamics, statistical thermodynamics and theories of electrolyte solutions, reaction networks, polymerization and catalysis.

The acid dissociation constant for an acid is a direct consequence of the underlying thermodynamics of the dissociation reaction ; the pK < sub > a </ sub > value is directly proportional to the standard Gibbs energy change for the reaction.

According to the second law of thermodynamics, a spontaneous reaction always results in an increase in total entropy of the system and its surroundings:

A Belousov – Zhabotinsky reaction, or BZ reaction, is one of a class of reactions that serve as a classical example of non-equilibrium thermodynamics, resulting in the establishment of a nonlinear chemical oscillator.

In thermodynamics, chemical potential, also known as partial molar free energy, is a form of potential energy that can be absorbed or released during a chemical reaction.

where is the activation barrier for the burning reaction and is the temperature developed as the result of burning ; the value of this so-called " flame temperature " can be determined from the laws of thermodynamics.

The second law of thermodynamics states that for any spontaneous process the overall ΔS must be greater than or equal to zero, yet a spontaneous chemical reaction can result in a negative change in entropy.

This means that the heat release of the chemical reaction sufficiently increases the entropy of the surroundings such that the overall entropy of the isolated system increases in accordance with the second law of thermodynamics.

While chemical kinetics is concerned with the rate of a chemical reaction, thermodynamics determines the extent to which reactions occur.

One fundamental difference between equilibrium thermodynamics and non-equilibrium thermodynamics lies in the behaviour of inhomogeneous systems, which require for their study knowledge of rates of reaction which are not considered in equilibrium thermodynamics of homogeneous systems.

In chemical thermodynamics, an endergonic reaction ( also called a nonspontaneous reaction or an unfavorable reaction ) is a chemical reaction in which the standard change in free energy is positive, and energy is absorbed.

After James Prescott Joule had determined the mechanical equivalent of heat, Lord Kelvin approached the question from an entirely different point of view, and in 1848 devised a scale of absolute temperature which was independent of the properties of any particular substance and was based solely on the fundamental laws of thermodynamics.

* Entropic forces: According to the second law of thermodynamics, a system progresses to a state in which entropy is maximized.

In most cases of interest in chemical thermodynamics there are internal degrees of freedom and processes, such as chemical reactions and phase transitions, which always create entropy unless they are at equilibrium, or are maintained at a " running equilibrium " through " quasi-static " changes by being coupled to constraining devices, such as pistons or electrodes, to deliver and receive external work.

William Thomson ( Lord Kelvin ) amalgamated all of these laws into the laws of thermodynamics, which aided in the rapid development of explanations of chemical processes by Rudolf Clausius, Josiah Willard Gibbs, and Walther Nernst.

In classical thermodynamics, the concept of entropy is defined phenomenologically by the second law of thermodynamics, which states that the entropy of an isolated system always increases or remains constant.

Thermodynamic entropy is more generally defined from a statistical thermodynamics viewpoint, in which the molecular nature of matter is explicitly considered.

Alternatively entropy can be defined from a classical thermodynamics viewpoint, in which the molecular interactions are not considered and instead the system is viewed from perspective of the gross motion of very large masses of molecules and the behavior of individual molecules is averaged and obscured.

Later, his lecture notes, especially those for quantum mechanics, nuclear physics, and thermodynamics, were transcribed into books which are still in print.

The holographic principle was inspired by black hole thermodynamics, which implies that the maximal entropy in any region scales with the radius squared, and not cubed as might be expected.

For example, advances in the understanding of electromagnetism or nuclear physics led directly to the development of new products which have dramatically transformed modern-day society, such as television, computers, domestic appliances, and nuclear weapons ; advances in thermodynamics led to the development of industrialization ; and advances in mechanics inspired the development of calculus.

Statistical mechanics or statistical thermodynamics is a branch of physics that applies probability theory, which contains mathematical tools for dealing with large populations, to the study of the thermodynamic behavior of systems composed of a large number of particles.

The fundamental concepts of heat capacity and latent heat, which were necessary for the development of thermodynamics, were developed by Professor Joseph Black at the University of Glasgow, where James Watt was employed as an instrument maker.

Thermodynamic systems are theoretical constructions used to model physical systems which exchange matter and energy in terms of the laws of thermodynamics.

Local equilibrium thermodynamics considers processes that involve the time-dependent production of entropy by dissipative processes, in which kinetic energy of bulk flow and chemical potential energy are converted into internal energy at time-rates that are explicitly accounted for.

Generalized thermodynamics might tackle such problems as ultrasound or shock waves, in which there are strong spatial inhomogeneities and changes in time fast enough to outpace a tendency towards local thermodynamic equilibrium.

The independent state variables of a small local region include flow rates, which are not admitted as independent variables for the small local regions of local equilibrium thermodynamics.

In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases ( gas, liquid, and solid ) of that substance coexist in thermodynamic equilibrium.

As it is customarily stated in textbooks, taken alone, the so-called ' zeroth law of thermodynamics ' fails to deliver this information, but the statement of the zeroth law of thermodynamics by James Serrin in 1977, though rather mathematically abstract, is more informative for thermometry: " Zeroth Law-There exists a topological line which serves as a coordinate manifold of material behaviour.