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Hess's law of constant heat summation, also known simply as Hess's law, is a relationship in physical chemistry and thermodynamics [1] 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 ...
Hess's law, in physical chemistry: the total enthalpy change during the complete course of a reaction is the same whether the reaction is made in one step or in several steps. Hick's law, in psychology, describes the time it takes for a person to make a decision as a function of the number of possible choices.
Scientific laws or laws of science are statements, based on repeated experiments or observations, that describe or predict a range of natural phenomena. [1] The term law has diverse usage in many cases (approximate, accurate, broad, or narrow) across all fields of natural science (physics, chemistry, astronomy, geoscience, biology).
A law of nature relevant to chemistry, such as the law of conservation of mass. chemical nomenclature chemical physics chemical process 1. Any method or means of changing one or more chemicals or chemical compounds in any way, either naturally or artificially, spontaneously or by the actions of external forces. 2.
Hess' law of constant heat summation (1840): The energy change accompanying any transformation is the same whether the process occurs in one step or many. [3] These statements preceded the first law of thermodynamics (1845) and helped in its formulation. Thermochemistry also involves the measurement of the latent heat of phase transitions.
The mass number (symbol A, from the German word: Atomgewicht, "atomic weight"), [1] also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus. It is approximately equal to the atomic (also known as isotopic) mass of the atom expressed in atomic mass units.
Every experiment to date has shown these seven values to be proportional, and in some cases equal, and this proportionality gives rise to the abstract concept of mass. There are a number of ways mass can be measured or operationally defined: Inertial mass is a measure of an object's resistance to acceleration when a force is applied. It is ...
In 1830, Hess took up chemistry full-time, researching and teaching, and later became an adjunct professor of Chemistry at the St. Petersburg Academy of Sciences. [1] His most famous paper, outlining his law on thermochemistry, was published there in 1840. [3] His principle, a progenitor for the first law of thermodynamics, came to be called ...