So we already spoke about a process called effusion which is the movement of gas molecules from a high pressure to a low pressure via a very small hole. And we said that we can find the rates at which gas molecules effuse via something called Grams law which is given right down here. And Grams law states that rate rate of gas molecule one over rate of gas molecule two is equal to the square root of mass of two divided by the square root of mass of one. And what this says is that the lighter the molecule, the faster its rate or the higher its rate. Now we're going to talk about something called diffusion. Diffusion is the movement or the flux of one type of gas molecule into another gas or an empty space.