Answer the following question given this paragraph: 

Figure 9.28 Diffusion occurs when gas molecules disperse throughout a container. Effusion occurs when a gas passes through an opening that is smaller than the mean free path of the particles, that is, the average distance traveled between collisions. Effectively, this means that only one particle passes through at a time.


Q: What occurs when a gas passes through an opening that is smaller than the mean free path of the particles?


A:
effusion