# Rate of hydrogenation

The rate of hydrogenation is faster for which alkene : cis or trans. I know it depends on steric hindrance on the carbon, but both have steric hindrance. Can someone please help

Imagine that the mechanism for the addition of $\ce{H-Hal}$, $\ce{Hal-Hal}$, and $\ce{H-H}$ to an alkene are fundamentally different.
In the first case, subsequent addition of the proton and (then) the halogen is assumed. In the second case, formation of a halonium ion is postulated as the first step, followed by addition of the halide (sort of backside attack to the existing $\ce{C-Hal}$ bond).