II. Graham’s Law of Diffusion & Effusion

A. Kinetic Energy The average kinetic energy of molecules is directly proportional to the absolute temperature

A. Kinetic Energy KE = ½ mv2 KE = kinetic energy m = mass v = velocity **At any given temperature, the molecules of ALL gases have the same average kinetic energy

B. Diffusion vs. Effusion Diffusion – tendency of molecules to move towards area of lower concentration until the concentration is uniform throughout

B. Diffusion vs. Effusion Effusion – the movement of gas particles through a small hole

B. Diffusion vs. Effusion

C. Comparison of Molecules

C. Comparison of Molecules Image two gas samples, one of He (4 g/mol) and one of Ne (20 g/mol). If both have a kinetic energy of 2 J, what speed are both moving at? Use KE = ½ mv2 He: 2 J = ½ (4 g) x v2 Ne: 2 J = ½ (20 g) x v2

HEAVIER GAS PARTICLES MOVE (DIFFUSE & EFFUSE) SLOWER

D. Graham’s Law Recall: If 2 gases (A and B) are at the same temperature, the molecules have the same average kinetic energy. KEA = KEB ½ mAvA2 = ½ mBvB

D. Graham’s Law of Diffusion Example: Mixture of He (4 g/mol) and Ne (20.2 g/mol)

Find the ratio of diffusion rates of O2 and N2 Graham’s Law Example Find the ratio of diffusion rates of O2 and N2