Exothermic reaction

As exothermic reaction refers to a chemical is delivered at the energy, e.g. in the form of heat to the environment. The contrast is the endothermic reaction. In an exothermic reaction, the so-called reaction enthalpy is negative. Enthalpy is the sum of the internal energy of the system and the product of pressure and volume. It is of the heat content in the system at constant pressure.

The term exothermic is not to be confused with the term exergonic (see definition).

Typical exothermic reactions are:

• Fire (combustion ) and
• Setting ( = hardening ) of concrete.

Exothermic, although to a much lesser extent, often extending well mixing of substances ( heat of mixing ) or the adsorption and absorption of substances such as on activated carbon or zeolite.

Identifies the difference between the enthalpies of the end () and raw materials (), so the energy absorbed, apply for exothermic reactions.

In physics, refers to a nuclear reaction in which energy is released as exothermic. An exothermic nuclear fusion is about hydrogen burning, as it happens in the sun.

Expiration

The reactants are initially in a metastable state. Due to short supply of a certain amount of energy, the activation energy ( activation energy ) will be brought the system into the unstable state. By activating the reaction gets going and runs without further energy input independently. In the overall balance the chemical system gives energy to the environment, it is called a reaction enthalpy. The products are now in a stable condition. On the stability of systems see system properties.

An example of adding the activation energy is the kindling of fire by rubbing a match at the friction surface or, for gases with an electrical spark.

For example, carbon is burned with oxygen in the air with evolution of heat to carbon dioxide.

The reaction enthalpy ( enthalpy ) of this reaction is negative. You can be calculated from the standard enthalpies.

If the activation energy is high, the reaction proceeds without any additional power supply not or only very slowly: The reaction is kinetically inhibited. Is the activation energy is low, the reaction can already be set in motion from the outside without any additional energy input. The activation energy is then withdrawn from the area.

Demarcation

When one speaks of an exothermic process, no statement is made as to whether a reaction takes place voluntarily. Here one then distinguishes between exergonic and endergonic reactions.