Concentrated sulfuric acid also adds across the double bond. The reaction occurs at room temperature and is a exothermic reaction (meaning it produces heat)
E.g.
Basically: electrophile - partially charged hydrogen atom in the sulfuric acid .
Carbocation which forms then very quickly with the negatively charged hydrogen sulfate ion
When water is added to the product an alcohol is formed and sulfuric acid is reformed
http://www.docbrown.info/page06/OrgMechs1b.htm#sulphuric
