Effusion differs from diffusion because effusion specifically involves passage through:

1. The two processes are explicitly described as similar but distinct. 2. A process involving movement of gaseous species similar to diffusion is effusion. 3. Effusion is the escape of gas molecules through a tiny hole, such as a pinhole in a balloon, into a vacuum. 4. Diffusion is spreading out within a space, ending in equal concentrations of gas throughout. 5. Neither process requires a solid metal barrier or a liquid layer. _Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 9 'Gases', sections 9.1-9.6_