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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 ...
Suppose : is a function taking as input a vector and outputting a scalar (). If all second-order partial derivatives of exist, then the Hessian matrix of is a square matrix, usually defined and arranged as = [].
For many substances, the formation reaction may be considered as the sum of a number of simpler reactions, either real or fictitious. The enthalpy of reaction can then be analyzed by applying Hess' law, which states that the sum of the enthalpy changes for a number of individual reaction steps equals the enthalpy change of the overall reaction.
Germain Henri Hess (Russian: Герман Иванович Гесс, romanized: German Ivanovich Gess; 7 August 1802 – 12 December [O.S. 30 November] 1850) was a Swiss-Russian chemist and doctor who formulated Hess' law, an early principle of thermochemistry.
Ludwig Otto Hesse (22 April 1811 – 4 August 1874) was a German mathematician.Hesse was born in Königsberg, Prussia, and died in Munich, Bavaria.He worked mainly on algebraic invariants, and geometry.
To convert intensity [W/sr/m 2] to flux [W/m 2], calculations usually invoke the "two-stream" and "plane parallel" approximations. [13] [18] The radiative flux is decomposed into three components, upward (+z), downward (-z), and parallel to the surface. This third component contributes nothing to heating or cooling the planet.
A Born–Haber cycle applies Hess's law to calculate the lattice enthalpy by comparing the standard enthalpy change of formation of the ionic compound (from the elements) to the enthalpy required to make gaseous ions from the elements. This lattice calculation is complex.
A third body (generally known as a planetoid), assumed massless with respect to the other two, moves in the plane defined by the two revolving bodies and, while being gravitationally influenced by them, exerts no influence of its own. [4]: 11 Per Barrow-Green, "[t]he problem is then to ascertain the motion of the third body." [4]: 11