The red end of the spectrum.
Concentrated sulfuric acid is used to promote acid catalyzed dehydration because it has little water.This favor the forward reaction.sulfuric acid acts as as proton source to enable loss of leaving group in forward reaction and electrophile addition in reverse reaction.
Please, observe that it is not right to say that a substance content heat.
Heat is not something that a body or substance content. Heat is the transmission of energy due to difference of temperatures.
An endothermic reactions is that where the reactants abosorb energy from the surroundings to occur. The products, then, will be higher in energy than the reactants while the surroundings get colder.
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