Grahams Law of Diffusion Grahams Law of Diffusion

  • Slides: 18
Download presentation
Graham’s Law of Diffusion

Graham’s Law of Diffusion

Graham’s Law of Diffusion NH 4 Cl(s) HCl 100 cm NH 3 100 cm

Graham’s Law of Diffusion NH 4 Cl(s) HCl 100 cm NH 3 100 cm Choice 1: Both gases move at the same speed and meet in the middle.

Diffusion NH 4 Cl(s) HCl 81. 1 cm NH 3 118. 9 cm Choice

Diffusion NH 4 Cl(s) HCl 81. 1 cm NH 3 118. 9 cm Choice 2: Lighter gas moves faster; meet closer to heavier gas.

Graham’s Law Consider two gases at same temp. Gas 1: KE 1 = ½

Graham’s Law Consider two gases at same temp. Gas 1: KE 1 = ½ m 1 v 12 Gas 2: KE 2 = ½ m 2 v 22 Since temp. is same, then… KE 1 = KE 2 ½ m 1 v 12 = ½ m 2 v 22 m 1 v 12 = m 2 v 22 Divide both sides by m 1 v 22… Take square root of both sides to get Graham’s Law:

Graham’s Law Diffusion – Spreading of gas molecules throughout a container until evenly distributed.

Graham’s Law Diffusion – Spreading of gas molecules throughout a container until evenly distributed. Effusion – Passing of gas molecules through a tiny opening in a container Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

Graham’s Law Speed of diffusion/effusion – Kinetic energy is determined by the temperature of

Graham’s Law Speed of diffusion/effusion – Kinetic energy is determined by the temperature of the gas. – At the same temp & KE, heavier molecules move more slowly. • Larger m smaller v KE = 2 ½mv Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

Graham’s Law – Rate of diffusion of a gas is inversely related to the

Graham’s Law – Rate of diffusion of a gas is inversely related to the square root of its molar mass. – The equation shows the ratio of Gas A’s speed to Gas B’s speed. Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

35 Br 79. 904 36 Graham’s Law Kr 83. 80 Determine the relative rate

35 Br 79. 904 36 Graham’s Law Kr 83. 80 Determine the relative rate of diffusion for krypton and bromine. The first gas is “Gas A” and the second gas is “Gas B”. Relative rate mean find the ratio “v. A/v. B”. Kr diffuses 1. 381 times faster than Br 2. Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

H 1 1. 00794 Graham’s Law O 8 15. 9994 A molecule of oxygen

H 1 1. 00794 Graham’s Law O 8 15. 9994 A molecule of oxygen gas has an average speed of 12. 3 m/s at a given temp and pressure. What is the average speed of hydrogen molecules at the same conditions? Put the gas with the unknown speed as “Gas A”. Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

H 2. 0 1 Graham’s Law O 8 15. 9994 An unknown gas diffuses

H 2. 0 1 Graham’s Law O 8 15. 9994 An unknown gas diffuses 4. 0 times faster than O 2. Find its molar mass. The first gas is “Gas A” and the second gas is “Gas B”. The ratio “v. A/v. B” is 4. 0. Square both sides to get rid of the square root sign. Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

Graham's Law http: //www. unit 5. org/christjs/temp T 27 d. Fields-Jeff/Gas. Law 1. htm

Graham's Law http: //www. unit 5. org/christjs/temp T 27 d. Fields-Jeff/Gas. Law 1. htm

Diffusion

Diffusion

Gas Diffusion and Effusion Graham's law governs effusion and diffusion of gas molecules. Rate

Gas Diffusion and Effusion Graham's law governs effusion and diffusion of gas molecules. Rate of effusion is inversely proportional to its molar mass. Thomas Graham (1805 - 1869)

To use Graham’s Law, both gases must be at same temperature. diffusion: particle movement

To use Graham’s Law, both gases must be at same temperature. diffusion: particle movement from diffusion high to low concentration NET MOVEMENT NET effusion: diffusion of gas particles effusion through an opening For gases, rates of diffusion & effusion obey Graham’s law: more massive = slow; less massive = fast

Diffusion Particles in regions of high concentration spread out into regions of low concentration,

Diffusion Particles in regions of high concentration spread out into regions of low concentration, filling the space available to them.

Weather and Diffusion LOW Air Pressure HIGH Air Pressure Map showing tornado risk in

Weather and Diffusion LOW Air Pressure HIGH Air Pressure Map showing tornado risk in the U. S. Highest High

Calculation of Diffusion Rate NH 3 V 1 = X M 1 = 17

Calculation of Diffusion Rate NH 3 V 1 = X M 1 = 17 amu HCl V 2 = X M 2 = 36. 5 amu Substitute values into equation V 1 moves 1. 465 x for each 1 x move of V 2 NH 3 HCl 1. 465 x + 1 x = 2. 465 200 cm / 2. 465 = 81. 1 cm for x

Calculation of Diffusion Rate V 1 m 2 = V 2 m 1 NH

Calculation of Diffusion Rate V 1 m 2 = V 2 m 1 NH 3 V 1 = X M 1 = 17 amu HCl V 2 = X M 2 = 36. 5 amu Substitute values into equation V 1 36. 5 = V 2 17 V 1 = 1. 465 V 2 V 1 moves 1. 465 x for each 1 x move of v 2 NH 3 HCl 1. 465 x + 1 x = 2. 465 200 cm / 2. 465 = 81. 1 cm for x