Alkenes react with gaseous hydrogen halides or hydrogen halides in solution (acids) at room temperature. Unsymmetrical alkenes give two products: a major product and a minor product which are isomers.Markownikoff's rule can be used to predict which isomer is the major product. It states that the hydrogen of the hydrogen halide attaches to the carbon atom with the most hydrogen atoms attached.The reason for more of the major product being formed is the greater stability of the secondary carbocation intermediate formed. Alkyl groups are electron-releasing so the positive charge being spread out over more alkyl groups leads to greater stability. 