Question

why does heat evovle when we add conc. sulphuric acid in water​

Answer 1

Beacuse its an exothermic reaction

Answer 2

And because the reaction happens so quickly, the amount of heat generated is released all at once, making the solution extremely hot. Because the hydration reaction of sulfuric acid is highly exothermic, dilution should always be performed by adding the acid to the water rather than the water to the acid.