What effect would a barrier island have on shoreline of the mainland?

It protects the coast from the raw ocean, it cuts waves off, and depending on how big the island is, could stop a tsunami

So  if  the sum of the enthalpies of the reactants is greater than the products, the  reaction  will be  exothermic.  if  the products side has a larger enthalpy, the  reaction  is  endothermic. you may wonder why  endothermic reactions, which soak up energy or enthalpy from the environment, even happen

Answerglycogen;