In equation He +Br2------>2HI why chemical rate of Br2 is taken as 1/2 . It's a reversible reaction. Please explain in detail. While H2 rate is taken as 1 why?

Answer 1

He +Br2------>2HI ?????? Just what have you been doing all night?

H2+Br2>>>>2HBr
So the rate of Br2 as 1/2 power? Maybe because the reaction is simplified, because if you look at it in more detail, it is to 3/2 power.
http://www.esf.edu/chemistry/dibble/fch361/info/H2Br2PSSA.pdf