Alkenes are characterized by a C-C double bond. The double bond is electron-rich. The pi bond behaves as a nucleophile and reacts with strong acids (electrophiles) to give addition products. The videos below present the data and then a mechanism that explains the experimental evidence, our best guess to what is going on at the molecular level.
HX acids (HI, HCl, and HBr) react with alkenes to give alkyl halides.
Water and acid react with alkenes to give alcohols.
Alcohols and acid react with alkenes to give ethers. This reaction is nearly identical to the addition of water!