2. Grahams Law

3. Molecules at the same temperature have the same average kinetic energy. (T KE) KE is proportional to the speed of the molecules and the mass of the molecules. KE = ½ mv 2

4. Grahams Law Diffusion – a gas spreading out Grahams Law deals with the effusion of two gases into each other. Effusion – a gas moving through a small hole

5. Grahams Law Gas A Gas B Consider two gases at the same temperature and pressure in a box with two partitions, separated by a wall with a hole that can be opened.

6. Grahams Law Gas A Gas B Gas A effuses into Gas B, and … Gas B effuses into Gas A, so that … …eventually both gases will be evenly distributed in the box.

7. Grahams Law Gas A Gas B The ratio of the rates at which Gas A and Gas B effuse into each other is … … inversely proportional to the square roots of their molar masses.

8. Grahams Law Gas A Gas B The bottom line: the lighter the gas, the faster it moves!

9. Grahams Law Gas A Gas B Suppose nitrogen and an unknown gas, both at the same temperature and pressure, are in the box. The rates of effusion are …

10. Grahams Law Gas A Gas B … 0.0160 moles/L/min for the nitrogen and 0.0205 mol/L/min for the unknown. What is the molecular weight of the unknown?

11. Grahams Law Gas A Gas B Start with the equation for Grahams Law

12. Grahams Law Gas A Gas B Square both sides, then solve for the molecular mass of compound x

13. Grahams Law Gas A Gas B

14. Grahams Law Gas A Gas B M x = 17.0g/mol

15. Grahams Law Gas A Gas B What is the unknown gas? The gas is smelly, dissolves in water to make a basic solution, and has a molar mass of 17 g/mol.

16. Grahams Law Gas A Gas B Ammonia gas, NH 3, has a strong smell, and...

17. OH - Grahams Law Gas A Gas B … it reacts with water … … it reacts with water … NH 3 (g) + HOH(l) NH 3 (g) + HOH(l) … which is a basic solution, OH - NH 4 + +

18. Grahams Law Gas A Gas B 1 x 14.0 + 3 x 1.0 = 17.0 g/mol … and ammonia, NH 3, has a molar mass of 17.0 g/mol.