Endothermic process

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An endothermic process is a chemical or physical process that absorbs heat from its surroundings. [1] In terms of thermodynamics, it is a thermodynamic process with an increase in the enthalpy H (or internal energy U) of the system. [2] In an endothermic process, the heat that a system absorbs is thermal energy transfer into the system. Thus, an endothermic reaction generally leads to an increase in the temperature of the system and a decrease in that of the surroundings. [1]

Contents

The term was coined by 19th-century French chemist Marcellin Berthelot. [3] The term endothermic comes from the Greek ἔνδον (endon) meaning 'within' and θερμ- (therm) meaning 'hot' or 'warm'. [4]

An endothermic process may be a chemical process, such as dissolving ammonium nitrate (NH4NO3) in water (H2O), or a physical process, such as the melting of ice cubes. [5]

The opposite of an endothermic process is an exothermic process, one that releases or "gives out" energy, usually in the form of heat and sometimes as electrical energy. [1] Thus, endo in endothermic refers to energy or heat going in, and exo in exothermic refers to energy or heat going out. In each term (endothermic and exothermic) the prefix refers to where heat (or electrical energy) goes as the process occurs. [6]

In chemistry

The formation of barium thiocyanate from ammonium thiocyanate and barium hydroxide is so endothermic that it can freeze a beaker to wet styrofoam

Due to bonds breaking and forming during various processes (changes in state, chemical reactions), there is usually a change in energy. If the energy of the forming bonds is greater than the energy of the breaking bonds, then energy is released. This is known as an exothermic reaction. However, if more energy is needed to break the bonds than the energy being released, energy is taken up. Therefore, it is an endothermic reaction. [7]

Details

Whether a process can occur spontaneously depends not only on the enthalpy change but also on the entropy change (∆S) and absolute temperature T. If a process is a spontaneous process at a certain temperature, the products have a lower Gibbs free energy G = H – TS than the reactants (an exergonic process), [2] even if the enthalpy of the products is higher. Thus, an endothermic process usually requires a favorable entropy increase (∆S > 0) in the system that overcomes the unfavorable increase in enthalpy so that still ∆G < 0. While endothermic phase transitions into more disordered states of higher entropy, e.g. melting and vaporization, are common, spontaneous chemical processes at moderate temperatures are rarely endothermic. [8] The enthalpy increase ∆H ≫ 0 in a hypothetical strongly endothermic process usually results in ∆G = ∆H – T∆S > 0, which means that the process will not occur (unless driven by electrical or photon energy). An example of an endothermic and exergonic process is

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Examples

Distinction between endothermic and endotherm

The terms "endothermic" and "endotherm" are both derived from Greek ἔνδονendon "within" and θέρμηthermē "heat", but depending on context, they can have very different meanings.

In physics, thermodynamics applies to processes involving a system and its surroundings, and the term "endothermic" is used to describe a reaction where energy is taken "(with)in" by the system (vs. an "exothermic" reaction, which releases energy "outwards"). [12] [13]

In biology, thermoregulation is the ability of an organism to maintain its body temperature, and the term "endotherm" refers to an organism that can do so from "within" by using the heat released by its internal bodily functions (vs. an "ectotherm", which relies on external, environmental heat sources) to maintain an adequate temperature. [14]

Related Research Articles

Chemical thermodynamics is the study of the interrelation of heat and work with chemical reactions or with physical changes of state within the confines of the laws of thermodynamics. Chemical thermodynamics involves not only laboratory measurements of various thermodynamic properties, but also the application of mathematical methods to the study of chemical questions and the spontaneity of processes.

<span class="mw-page-title-main">Chemical reaction</span> Process that results in the interconversion of chemical species

A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products are generated. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei, and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur.

<span class="mw-page-title-main">Exothermic process</span> Thermodynamic process that releases energy to its surroundings

In thermodynamics, an exothermic process is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light, electricity, or sound. The term exothermic was first coined by 19th-century French chemist Marcellin Berthelot.

<span class="mw-page-title-main">Enthalpy</span> Measure of energy in a thermodynamic system

Enthalpy is the sum of a thermodynamic system's internal energy and the product of its pressure and volume. It is a state function in thermodynamics used in many measurements in chemical, biological, and physical systems at a constant external pressure, which is conveniently provided by the large ambient atmosphere. The pressure–volume term expresses the work that was done against constant external pressure to establish the system's physical dimensions from to some final volume , i.e. to make room for it by displacing its surroundings. The pressure-volume term is very small for solids and liquids at common conditions, and fairly small for gases. Therefore, enthalpy is a stand-in for energy in chemical systems; bond, lattice, solvation, and other chemical "energies" are actually enthalpy differences. As a state function, enthalpy depends only on the final configuration of internal energy, pressure, and volume, not on the path taken to achieve it.

<span class="mw-page-title-main">Thermochemistry</span> Study of the heat energy associated with chemical reactions and/or physical transformations

Thermochemistry is the study of the heat energy which is associated with chemical reactions and/or phase changes such as melting and boiling. A reaction may release or absorb energy, and a phase change may do the same. Thermochemistry focuses on the energy exchange between a system and its surroundings in the form of heat. Thermochemistry is useful in predicting reactant and product quantities throughout the course of a given reaction. In combination with entropy determinations, it is also used to predict whether a reaction is spontaneous or non-spontaneous, favorable or unfavorable.

<span class="mw-page-title-main">Enthalpy of vaporization</span> Energy to convert a liquid substance to a gas at a given pressure

In thermodynamics, the enthalpy of vaporization, also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (enthalpy) that must be added to a liquid substance to transform a quantity of that substance into a gas. The enthalpy of vaporization is a function of the pressure and temperature at which the transformation takes place.

<span class="mw-page-title-main">Thermodynamic free energy</span> State function whose change relates to the systems maximal work output

In thermodynamics, the thermodynamic free energy is one of the state functions of a thermodynamic system. The change in the free energy is the maximum amount of work that the system can perform in a process at constant temperature, and its sign indicates whether the process is thermodynamically favorable or forbidden. Since free energy usually contains potential energy, it is not absolute but depends on the choice of a zero point. Therefore, only relative free energy values, or changes in free energy, are physically meaningful.

In chemistry, the standard molar entropy is the entropy content of one mole of pure substance at a standard state of pressure and any temperature of interest. These are often chosen to be the standard temperature and pressure.

<span class="mw-page-title-main">Gibbs free energy</span> Type of thermodynamic potential

In thermodynamics, the Gibbs free energy is a thermodynamic potential that can be used to calculate the maximum amount of work, other than pressure-volume work, that may be performed by a thermodynamically closed system at constant temperature and pressure. It also provides a necessary condition for processes such as chemical reactions that may occur under these conditions. The Gibbs free energy is expressed asWhere:

<span class="mw-page-title-main">Hess's law</span> Observation that total enthalpy change of a chemical reaction is independent of the steps taken

Hess’ law of constant heat summation, also known simply as Hess' law, is a relationship in physical chemistry and thermodynamics named after Germain Hess, a Swiss-born Russian chemist and physician who published it in 1840. The law states that the total enthalpy change during the complete course of a chemical reaction is independent of the sequence of steps taken.

In thermodynamics, a spontaneous process is a process which occurs without any external input to the system. A more technical definition is the time-evolution of a system in which it releases free energy and it moves to a lower, more thermodynamically stable energy state. The sign convention for free energy change follows the general convention for thermodynamic measurements, in which a release of free energy from the system corresponds to a negative change in the free energy of the system and a positive change in the free energy of the surroundings.

Chemical energy is the energy of chemical substances that is released when the substances undergo a chemical reaction and transform into other substances. Some examples of storage media of chemical energy include batteries, food, and gasoline. Breaking and re-making chemical bonds involves energy, which may be either absorbed by or evolved from a chemical system. If reactants with relatively weak electron-pair bonds convert to more strongly bonded products, energy is released. Therefore, relatively weakly bonded and unstable molecules store chemical energy.

<span class="mw-page-title-main">Exergonic reaction</span> Chemical reaction that releases more energy than was needed to start it

In chemical thermodynamics, an exergonic reaction is a chemical reaction where the change in the free energy is negative. This indicates a spontaneous reaction if the system is closed and initial and final temperatures are the same. For processes that take place in a closed system at constant pressure and temperature, the Gibbs free energy is used, whereas the Helmholtz energy is relevant for processes that take place at constant volume and temperature. Any reaction occurring at constant temperature without input of electrical or photon energy is exergonic, according to the second law of thermodynamics. An example is cellular respiration.

<span class="mw-page-title-main">Endergonic reaction</span> Chemical reaction which requires more energy to initiate than it produces

In chemical thermodynamics, an endergonic reaction is a chemical reaction in which the standard change in free energy is positive, and an additional driving force is needed to perform this reaction. In layman's terms, the total amount of useful energy is negative so the total energy is a net negative result, as opposed to a net positive result in an exergonic reaction. Another way to phrase this is that useful energy must be absorbed from the surroundings into the workable system for the reaction to happen.

<span class="mw-page-title-main">Exothermic reaction</span> Chemical reaction that releases energy as light or heat

In thermochemistry, an exothermic reaction is a "reaction for which the overall standard enthalpy change ΔH⚬ is negative." Exothermic reactions usually release heat. The term is often confused with exergonic reaction, which IUPAC defines as "... a reaction for which the overall standard Gibbs energy change ΔG⚬ is negative." A strongly exothermic reaction will usually also be exergonic because ΔH⚬ makes a major contribution to ΔG⚬. Most of the spectacular chemical reactions that are demonstrated in classrooms are exothermic and exergonic. The opposite is an endothermic reaction, which usually takes up heat and is driven by an entropy increase in the system.

In thermochemistry, a thermochemical equation is a balanced chemical equation that represents the energy changes from a system to its surroundings. One such equation involves the enthalpy change, which is denoted with ΔH. In variable form, a thermochemical equation would appear similar to the following:

An exergonic process is one which there is a positive flow of energy from the system to the surroundings. This is in contrast with an endergonic process. Constant pressure, constant temperature reactions are exergonic if and only if the Gibbs free energy change is negative (∆G < 0). "Exergonic" means "releasing energy in the form of work". In thermodynamics, work is defined as the energy moving from the system to the surroundings during a given process.

The Van 't Hoff equation relates the change in the equilibrium constant, Keq, of a chemical reaction to the change in temperature, T, given the standard enthalpy change, ΔrH⊖, for the process. The subscript means "reaction" and the superscript means "standard". It was proposed by Dutch chemist Jacobus Henricus van 't Hoff in 1884 in his book Études de Dynamique chimique.

In thermodynamics, the enthalpy of mixing is the enthalpy liberated or absorbed from a substance upon mixing. When a substance or compound is combined with any other substance or compound, the enthalpy of mixing is the consequence of the new interactions between the two substances or compounds. This enthalpy, if released exothermically, can in an extreme case cause an explosion.

In chemistry, thermochemical cycles combine solely heat sources (thermo) with chemical reactions to split water into its hydrogen and oxygen components. The term cycle is used because aside of water, hydrogen and oxygen, the chemical compounds used in these processes are continuously recycled.

References

  1. 1 2 3 "17.3: Exothermic and Endothermic Processes". Chemistry LibreTexts. 2016-06-27. Retrieved 2024-06-26.
  2. 1 2 Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015). Principle of Modern Chemistry , Brooks Cole. p. 617. ISBN   978-1305079113
  3. ↑ Sutton, Mike (2007-03-01). "Chemistry for the common good". Chemistry World. Retrieved 2024-06-26.
  4. ↑ "endothermic | Etymology of endothermic by etymonline". www.etymonline.com. Retrieved 2024-06-28.
  5. ↑ Lu, Jue Xi; Tupper, Connor; Gutierrez, Alejandra V.; Murray, John (2024), "Biochemistry, Dissolution and Solubility", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID   28613752 , retrieved 2024-06-28
  6. ↑ "Endothermic & Exothermic Reactions" (PDF). Ashrae. Retrieved 2024-06-28.
  7. ↑ "Exothermic & Endothermic Reactions". Energy Foundations for High School Chemistry. American Chemical Society. Retrieved 2021-04-11.
  8. ↑ "Examples of Spontaneous Endothermic Reactions - Chemistry Examples". www.chemicool.com. Retrieved 2024-06-28.
  9. ↑ "Galactic nucleosynthesis: the onset of element production in our galaxy". Research Features. 2017-05-15. Retrieved 2024-06-28.
  10. ↑ Austin, Patrick (January 1996). "Tritium: The environmental, health, budgetary, and strategic effects of the Department of Energy's decision to produce tritium". Institute for Energy and Environmental Research . Retrieved 2010-09-15.
  11. ↑ Qian, Y.-Z.; Vogel, P.; Wasserburg, G. J. (1998). "Diverse Supernova Sources for the r-Process". Astrophysical Journal 494 (1): 285–296. arXiv : astro-ph/9706120. Bibcode : 1998ApJ...494..285Q. doi : 10.1086/305198.
  12. ↑ "5.2: The First Law of Thermodynamics". Chemistry LibreTexts. 2014-11-18. Retrieved 2024-06-28.
  13. ↑ "Meaning of endothermic in English". Cambridge Dictionary. Cambridge University Press.
  14. ↑ "Endotherm | Homeothermy, Thermoregulation, Metabolism | Britannica". www.britannica.com. Retrieved 2024-06-28.
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