When two aqueous solutions are mixed together and the temperature of the solution decreases, the reaction is called an endothermic reaction with a positive enthalpy change. Endothermic reaction is when heat is absorbed by the reaction taking place. All endothermic reaction always have a positive enthalpy change.
Esters contains a double bond between carbon atom and oxygen atom while carboxylic acid lack double bond between carbon and oxygen atom.The lack of double bond in carboxylic acid make the force of interaction between carbon and oxygen strong and particles become tightly packed which make carboxylic acid solid. The presence of double bond in esters make the force of interaction weak thus they are liquid.
Theyre the big bunched up group in the middle of the periodic table
