An endothermic reaction.
Endothermic reaction – a chemical reaction accompanied by absorption of heat. Endothermic reaction absorbs heat from the external environment. That is, the energy required to initiate a chemical reaction, more emitted energy.
Examples of endothermic reactions
Endothermic reaction is a chemical reaction accompanied by absorption of heat. It is the opposite of an exothermic reaction.
Endothermic reaction absorbs heat from the external environment. That is, the energyneeded to initiate chemical reactions, more 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 endothermic reaction, by definition, the enthalpy change (ΔH) is positive:
ΔH > 0,
since a larger value (the energyused for the reaction) is subtracted from a smaller value (the energy released in the reaction).
At thermal decomposition of carbonate of calcium, for example:
CaCO3 → CaO + CO2 177,9 kJ occurring at a temperature of 900-1200 °C,
the enthalpy change equal to ∆ H = 177,9 kJ per one mole of CaCO3.
Consumed during endothermic reactions energy is measured in joules per mole. The reaction has a positive value of ΔH (change in heat) because of the cost of heat. example: 177,9 j/mol, like in the above example.
Examples of endothermic reactions:
– restoration of metals from oxides,
– electrolysis (absorbed electric energy),
– electrolytic dissociation (e.g., dissolution of salts in water),
Source: https://ru.wikipedia.org/wiki/Экзотермические_реакции, https://ru.wikipedia.org/wiki/Эндотермические_реакции
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