Endothermic

As endothermic chemical reactions are referred to, in which energy must be supplied. The Standardenthalpiedifferenz is positive. The enthalpy H is the sum of the internal energy of the system and the product of pressure and volume. It is the heat content of a system at constant pressure. An endothermic reaction, therefore, a response is received at the energy in the form of heat from the environment. It is the opposite of an exothermic reaction dar. Identifies the difference between the enthalpies of the end () and raw materials (), so the absorbed energy, valid for endothermic reactions.

Expiration of an endothermic reaction

As exothermic reactions, the process is carried out also in the endothermic reactions in two steps. First, a certain activation energy has to be applied, then a portion of this energy is released again. The difference from the exothermic reaction is the fact that this released energy is less than the activation energy and, therefore, is not sufficient to further advance the reaction. The reaction energy is positive. Therefore, in order not to interrupt the reaction, while the reaction energy to be continuously fed from the outside.

For an endothermic reaction can take place at all ( is exergonic ), the reaction by increasing the entropy must be favored and so have a negative free energy. Endothermic reactions therefore often take place at high temperatures, as these according to the Gibbs -Helmholtz equation, the entropic contribution to the free enthalpy is greater. This is shown for example on the Boudouard equilibrium, in which at high temperatures, the endothermic reaction takes place to carbon monoxide.

For example: Executes one of a coke layer water vapor, an endothermic reaction takes place: .

Industrial Chemistry

As allotherm endothermic reactions in industrial chemistry are referred to. Important examples of this are allothermal pyrolysis, in which the biomass is digested by externally supplied heat and the steam reforming in the production of synthesis gas. The contrast, in the industrial usage autothermal reactions.

Physics

In physics, accordingly, is called a nuclear reaction is endothermic if it can take place only with external power supply. The energy may be provided as kinetic energy of the initial reactants, in that they are accelerated to a high speed (see particle ). Other ways of energization are pressure and high temperature, for example in the nuclear fusion.