What happens when you mix KNO3 H2SO4?

When potassium nitrate (KNO3) is mixed with sulfuric acid (H2SO4), a reaction occurs which produces nitric acid (HNO3) and potassium bisulfate (KHSO4). The reaction is exothermic, releasing heat, and also releases nitrogen dioxide gas (NO2) as a byproduct. This reaction is often used in the laboratory to produce nitric acid.