Collision theory
= Collision theory
{wiki}
<Collision theory> estimates a gas-phase <reaction rate> by combining encounter frequency with energetic and geometrical requirements for reaction. For distinct hard spheres with contact separation $R$, the collision cross section is $\pi R^2$, and the mean relative speed is $\sqrt{8kT/(\pi\mu)}$. A reactive barrier and orientation restrictions reduce the fraction of collisions that react.