Which reactions are called exothermic and which are endothermic? How is the thermal effect of a reaction denoted in thermochemical

Which reactions are called exothermic and which are endothermic? How is the thermal effect of a reaction denoted in thermochemical equations? What reactions, exothermic or endothermic, are usually combustion and thermal decomposition reactions of salts?

Reactions with the release of heat are called exothermic (combustion reactions), with heat absorption – endothermic (salt decomposition reactions).
The heat effect of the reaction in thermochemical equations is denoted by the letter Q.

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