Many stone buildings are made from limestone, which is primarily valium carbonate. what happens to such buildings over time if they are exposed to acid rain?

They gradually dissolve.  

Step-by-step explanation:

The acids in acid rain react with the calcium carbonate.

For example,

CaCO₃ + 2HNO₃ ⟶ Ca(NO₃)₂ + H₂O + CO₂

The soluble calcium salts wash away.

The surfaces of the buildings become eroded and carved details gradually disappear.  

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.