1. Gases

2. Do Now Find the formula weight of SO 4 2- Mo(NO 3 ) 3 Find the amount of moles in 100g of Sulfate

3. Properties of Gases No defined shape- forms to container No defined volume Particles have high energy (moving quickly) Kinetic Molecular Theory: an ideal gas is composed of molecules, which are in constant motion – The average kinetic energy of the molecules is directly related to the temperature (in Kelvin) of the gas

4. Ideal Gases Ideal Gas: a theoretical gas in which the molecules are not interacting with each other The collisions of the molecules with the walls of the container are the cause of the pressure exerted by the gas

5. The Kelvin Scale Based on the concept of absolute zero: the temperature at which all molecular movement would cease Absolute Zero = 0 Kelvin 273K = 0°C To find a temperature in Kelvin, add 273 to the temperature in °C K = °C + 273

6. Practice with the Kelvin Scale If it’s 35°C, what is the temperature in Kelvin?

7. Practice with the Kelvin Scale If it’s 35°C, what is the temperature in Kelvin? K = °C + 273 K = 35 + 273 = 308 K

8. Practice with the Kelvin Scale If it’s -12°C, what is the temperature in Kelvin?

9. Practice with the Kelvin Scale If it’s -12°C, what is the temperature in Kelvin? K = °C + 273 K = -12 + 273 = 261 K

10. Practice with the Kelvin Scale If it’s 350 K, what is the temperature in Celsius?

11. Practice with the Kelvin Scale If it’s 350 K, what is the temperature in Celsius? K = °C + 273 350 = °C + 273 -273 77° = °C

12. STP: Standard Temperature and Pressure Standard Temperature = 0°C (273K) Standard Pressure = 1 atm. (760mm Hg = 760 torr) 1 mole of an ideal gas under standard conditions will have a volume = 22.4L

13. Atmospheric Pressure A barometer measures the pressure of the atmosphere (the force of the atmosphere pushing down on the earth due to gravity)

14. Atmospheric Pressure A Torricellian barometer is a glass tube filled with mercury. This tube is inverted in a dish that also contains mercury. The mercury flows out of the tube until the pressure of the column of mercury equals the pressure from the air pushing down on the mercury in the dish. At 1atm, the average height of the column of mercury is 760mm

15. Volume of a Gas We have 3mol of an ideal gas at STP. What is the volume?

16. Volume of a Gas We have 3mol of an ideal gas at STP. What is the volume? 3mol x 22.4L = 67.2L 1 1 mol

17. Volume of a Gas We have 8mol of an ideal gas at STP. What is the volume?

18. Volume of a Gas We have 8mol of an ideal gas at STP. What is the volume? 8mol x 22.4L = 179.2L 1 1 mol

19. Volume of a Gas We have 8 L of an ideal gas at STP. How many moles?

20. Volume of a Gas We have 5g of H 2 at STP. Assuming H 2 is an ideal gas, what is the volume?

21. Volume of a Gas We have 5g of H 2 at STP. Assuming H 2 is an ideal gas, what is the volume? 5g x 1mol x 22.4L = 56L 1 2g 1 mol

22. Exit Ticket #1

23. 1.If it is 27.5°C, what is the temperature in Kelvin? (2 points) 2.What does STP mean? (1 point) 3.What are the values of STP? (2 points) 4.What is the volume of 3.5mol of an ideal gas? (2 points) 5.You have 25g of nitrogen gas (molar mass = 28g/mol). At STP, what would the volume be? (3 points)

24. Gas Laws Quick Preview: – Ideal Gas Law – Boyle’s Law – Charles’ Law – Avogadro’s Law – Gay-Lussac’s Law

25. Ideal Gas Law A combination of the other gas laws into one general formula: PV = nRT P: pressure (atm) V: volume (L) n: number of moles R: gas constant = 0.08206 L  atm/K  mol T: temperature (K)

26. Ideal Gas Law Practice A sample of hydrogen gas (H 2 ) has a volume of 8.56L at 0°C and a pressure of 1.5atm. How many moles of H 2 gas are present?

27. Ideal Gas Law Practice A sample of hydrogen gas (H 2 ) has a volume of 8.56L at 0°C and a pressure of 1.5atm. How many moles of H 2 gas are present? K = °C + 273 = 0 + 273 = 273 K PV = nRT (1.5atm)(8.56L) = n(0.08206L  atm/K  mol)(273K) 12.84atm  L = n(22.4K  atm  L) K  mol22.4/mol = 0.57mol = n

28. Challenge Problem How could you change the original ideal gas law equation so that all of the VARIABLES are on one side, and the CONSTANTS are on another? – Hint: Imagine having a sample of a gas. What things could you change about that particular sample? – Write your answer on a sheet of paper to turn in for a chance at extra credit!

29. Ideal Gas Law 2 We can use the original ideal gas law to determine the initial and final conditions of a gas P 1 V 1 = R and R = P 2 V 2 T 1 n 1 T 2 n 2 Since R = R, we can combine these two equations into the following: P 1 V 1 = P 2 V 2 T 1 n 1 T 2 n 2

30. Ideal Gas Law 2 P 1 V 1 = P 2 V 2 T 1 n 1 T 2 n 2 Any variable that is a constant can immediately be cancelled out. *Look for things that aren’t mentioned in the problem, or things that don’t change from start to finish in the problem

31. Boyle’s Law The temperature and moles remain constant, leaving us with: P 1 V 1 = P 2 V 2

32. Charles’ Law The pressure and moles remain constant, leaving us with: V 1 = V 2 T 1 T 2

33. Avogadro’s Law The pressure and temperature remain constant, but the moles change (ex. due to different coefficients from the balanced reaction) V 1 = V 2 n 1 n 2

34. Gas Laws Practice P 1 V 1 = P 2 V 2 T 1 n 1 T 2 n 2 Example: you have a 5L sample of gas at a pressure of 1atm. What would the final volume be if the pressure was changed to 5.5atm? – What variables remain constant? What law does this agree with?

35. Gas Laws Practice P 1 V 1 = P 2 V 2 T 1 n 1 T 2 n 2 Example: you have a 5L sample of gas at a pressure of 1atm. What would the final volume be if the pressure was changed to 5.5atm? – What variables remain constant? What law does this agree with? –  TEMPERATURE and MOLES: BOYLE’S Law

36. Gas Laws Practice P 1 V 1 = P 2 V 2 T 1 n 1 T 2 n 2 Example: you have a 5L sample of gas at a pressure of 1atm. What would the final volume be if the pressure was changed to 5.5atm? P 1 V 1 = P 2 V 2 1atm  5L = 5.5atm  V 2 0.91L = V 2

37. Gas Laws Practice A 1.75L sample of an ideal gas is kept under STP conditions. If the temperature is changed to 325K, what is the final volume of the sample? – What variables are constant? What law does this follow?

38. Gas Laws Practice A 1.75L sample of an ideal gas is kept under STP conditions. If the temperature is changed to 325K, what is the final volume of the sample? – What variables are constant? What law does this follow? –  PRESSURE and MOLES constant: CHARLES’ Law

39. Gas Laws Practice A 1.75L sample of an ideal gas is kept under STP conditions. If the temperature is changed to 325K, what is the final volume of the sample? V 1 = V 2 T 1 T 2 1.75L = V 2  2.1L 273K325K

40. Gas Laws Practice A 3.25L sample of an ideal gas has an original temperature of 75°C. What is the original pressure if the sample is returned to STP conditions and has a final volume of 6L?

41. Gas Laws Practice A 3.25L sample of an ideal gas has an original temperature of 75°C. What is the original pressure if the sample is returned to STP conditions and has a final volume of 6L? K = 75 + 273 = 348K P 1 V 1 = P 2 V 2  P 1 3.25L = 1atm  6L T 1 T 2 348K273K P 1 = 2.35atm

42. Gas Laws Practice We have a 12.2L sample of 0.5mol O 2. If the reaction proceeds under STP conditions and all O 2 becomes O 3, what is the final volume? – NOTE: you will need to do stoich. to determine the 3 O 2  2 O 3 (Avogadro’s Law)

43. Gas Laws Practice We have a 12.2L sample of 0.5mol O 2. If the reaction proceeds under STP conditions and all O 2 becomes O 3, what is the final volume? – NOTE: you will need to do stoich. to determine the 3 O 2  2 O 3 (Avogadro’s Law) 0.5mol O 2  2mol O 3 = 0.33mol O 3 (n 2 ) 1 3 mol O 2

44. Gas Laws Practice We have a 12.2L sample of 0.5mol O 2. If the reaction proceeds under STP conditions and all O 2 becomes O 3, what is the final volume? V 1 = V 2 n 1 n 2 12.2L =V 2  8.1 L 0.5mol0.33mol

45. Exit Ticket #2

46. Complete the following problems, showing all work (including the original equation). Round answers to the nearest tenth. 1.How many moles of H 2 gas are present in 3L if the pressure is 1.75atm and the temperature is 25°C? (3 points) 2.A 2mol sample of H 2 gas is kept at a temperature of 280K and has a volume of 1.5L. What is the pressure in mm Hg? (3 points) 3.A sample of ideal gas has a volume of 1.25L at standard temperature. If the temperature is increased to 30°C, what is the final volume? (2 points) 4.An ideal gas has a volume of 0.75L at STP. What is the pressure if the volume decreases to 0.25L? (2 points)