Exothermic reaction

The exothermic reaction.



 

 

Exothermic reaction – a chemical reaction accompanied by release of heat. Exothermic reaction gives off heat energy to the external environment. That is, the energy required to initiate chemical reactions, is less than the emitted energy.

 

Exothermic reaction

Examples of exothermic reactions

 


Exothermic reaction:

Exothermic reaction – a chemical reaction accompanied by release of heat. It is the opposite of an endothermic reaction.

Exothermic reaction gives off heat energy to the external environment. That is, the energy required to initiate chemical reactions, is less than the emitted energy.


The absolute amount of energy in a chemical system is extremely difficult to measure or calculate. However, the enthalpy change (ΔH) of a chemical reaction is much easier to count.

ΔH = [energyspent to break bonds of reactants] – [energyallocated at formation of bonds of the products of chemical reactions].

For measuring ΔH using the calorimeters.

In an exothermic reactionby definition the enthalpy change (ΔH) is negative:

ΔH < 0,

since a larger value (the energyreleased in the reaction) is subtracted from a smaller value (the energyused for the reaction).

The combustion of hydrogen, for example:

2H2 + O2 → 2H2O + 483,6 kJ,

the enthalpy change equal to ∆ H = -483,6 kJ per one mole of O2.

Released during an exothermic reaction energy is measured in joules per mole. The reaction has a negative ΔH (change in heat) due to heat loss. Example: -483,6 j/mol, like in the above example.

 

Examples of exothermic reactions:

– the combustion of the fuel, gunpowder,

– addition of concentrated sulfuric acid in water,

– oxidation of fats and carbohydrates in living organisms,

– adiabatic combustion

– nuclear fission of uranium,

– the oxidation of metals,

– most of the polymerization reactions

respiration of living organisms,

– other.

 

Source: https://ru.wikipedia.org/wiki/Экзотермические_реакции

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