Question

What will happen if dilute h2so4 is not added to water

Answer 1

It seems the you have not question properly here. 
But if you don't add the dilute H2SO4 to water nothing will happen.
on the other hand if you add the sulfuric acid in to water this reaction will produce heat and result in a exothermic reaction. Normally if the sulfuric acid is concentrated and then added to water  that can result in an boiling of water and is a vigorous reaction which can also spit out and fall on your skin. But dilute Sulfuric acid  addition to water will not cause this much of  exothermic reaction as the acid is not pure this time. But it still depend on the dilution of acid . In order to avoid any danger normally the acid is added slowly to water in order to give it time for neutralization .

Answer 2

It seems that you have not completed your question here. So, I am giving every possible answer to this question.
If dilute H₂SO₄ is not added to water then no reaction takes place.
However, H₂SO₄ reacts very vigorously with water and is an exothermic reaction as a lot of heat and energy is emitted.
When H₂SO₄ is mixed with water, hydrogen ion is donated from sulphuric acid and hydronium ion is produced. H₂SO₄ becomes its conjugate base HSO₄⁻ .
The equation for the reaction is given as:
H₂SO₄ + H₂O → H₃O⁺ + HSO₄⁻
However it is important to note that always pour water first and then acid not vice versa. The reason is that otherwise the acid becomes very hot and splashing may happens.