The rate constant for the elementary reaction K + Br2 -> KBr + Br is 1.0 × 10^12 L mol^-1 s^-1 independent of temperature. Calculate the rate constant expected from collision theory at 298 K. The fact that the rate constant is greater than would be expected from collision theory is explained by the harpoon mechanism. According to this mechanism an electron jumps from K to Br2 when these two molecules come within a certain distance that is greater then the collision diameter d12, which is 400 pm.