1. Ch. 12 Behavior of Gases

2. Gases Gases expand to fill its container, unlike solids or liquids Easily compressible: measure of how much the volume of matter decreases under pressure

3. Variables that describe a gas Pressure (P) – Measured in kilopascals, kPa – Pressure and number of molecules are directly related increase molecules = increase pressure – Gases naturally move from areas of high pressure to low pressure, due to the available space to move into

4. Variables that describe a gas Volume (V) – Measured in Liters, L – Volume and pressure are inversely related As volume decreases, the pressure increases Smaller container = less room for movement, therefore molecules hit sides of container more often

5. Variables that describe a gas Temperature (T) – Measured in Kelvin, K – The temperature and pressure are directly related Increase in temp = increase in pressure Volume must be held constant Molecules hit the walls harder (due to increase in K.E.) and more frequently. Think about a tire in hot weather…

6. Variables that describe a gas Amount – Measured in moles, mol – Moles and pressure are directly related Increase in # of moles = increase in pressure Ex: Inflating a balloon is adding more molecules. Temperature must remain constant

7. Gas Laws Describe how gases behave Change can be calculated Know the math and the theory!!

8. Boyles Law (1662) Gas pressure is inversely related to volume (as volume increases, pressure decreases) Temperature is constant P 1 V 1 = P 2 V 2

9. Ex: The pressure of a 2.5L of gas changes from 105 kPa to 40.5 kPa. What will be the new volume?

10. Charless Law (1787)

11. Ex: A sample of Nitrogen occupies a volume of 250 mL at 25 o C. What volume will the gas occupy at 95 o C?

12. Gay-Lussacs Law (1802)

13. Ex: A gas has a pressure of 710 kPa at 227 o C. What will the pressure be at 27 o C, if the volume does not change?

14. Combined Gas Law

15. Ex: 3.0 L of Hydrogen gas has a pressure of 1.5 atm at 20 o C. What would the volume be if the pressure increased to 2.5 atm at 30 o C?

16. Ideal Gas Law

17. A gas behaves ideally if it conforms to the gas laws – Gases do not usually do this – Real gases only behave this way at: 1.High temps (molecules move fast) 2.Low pressure (molecules are far apart) This is because gases will stay a gas under these conditions – Molecules are not next to each other very long so attractive forces cant play a role b/c molecules are moving too fast – Ideal Gases do no exist because: 1.Molecules do take up space 2.There are attractive forces between molecules otherwise no liquid would form. (Molecules slow down to become liquids)

18. Ex: What volume will 2.0 mol of N 2 occupy at 720 torr and 20 o C?

19. Daltons Law of Partial Pressures Used for mixture of gases in a container If you know the P exerted by each gas in a mixture, you can calculate the total gas pressure It is particularly useful in calculating pressure of gases collected over water. P total = P 1 + P 2 + P 3 … *P1 represents the partial pressure or the contribution by the gas

20. Ex: Helium, Nitrogen, and Oxygen exist in a container. Calculate the total pressure of the mixture for the following partial pressures: He = 200 kPa N= 500 kPa O= 400 kPa

21. Grahams Law of Effusion