1. Gases
Chapter 10

2. Review Temperature Pressure Volume Number of Moles, n
Average kinetic energy
Pressure
Collisions of gas particles between each other and container walls
Volume
Amount of space
Number of Moles, n

3. Review
Boyle’s Law
Charles’s Law
Gay-Lussac’s Law
Avogadro’s Law

4. Boyle’s Law V P
Inverse

5. Charles’s Law T V
Direct

6. Gay-Lussac's Law T P
Direct

7. Avogadro’s Law n V
Direct

8. Kinetic Molecular Theory
The particles in a gas are constantly moving in rapid, random, straight-line motion.
Gas particles have no volume compared to the volume of the gas.
No attraction between particles
All collisions are completely elastic

9. All Together Now Constant
If we add Avogadro’s Law into the Combined Gas Law:
Constant

10. Ideal Gas Law
PV = nRT
R = Universal Gas Constant
Ideal Gases follow assumptions of the Kinetic Molecular Theory

11. Ideal Gases When do real gases act most like an ideal gas?
High Temperature
Low Pressure
When do real gases act least like an ideal gas?
Low Temperature
High Pressure

13. Units of Pressure Atmospheres (atm) Pound / inch2 (psi)
Pascal (Pa) = N/m2
millimeters of Mercury (mmHg)
Torr

14. Atmospheric pressure Pressure exerted by the air above us 1 atm
14.7 psi
kPa
760 mmHg or torr

15. Measuring Pressure Barometer Measures atmospheric pressure
Invented by Torricelli in 1600’s

16. Measuring Pressure
Manometer
Measures pressure in a sealed container

17. Ideal Gas Law
PV = nRT
R = Universal Gas Constant

18. 𝑃𝑉=𝑛𝑅𝑇 𝑉= 𝑛𝑅𝑇 𝑃 Molar Volume
1 mole of ANY gas occupies 22.4L of volume at STP
𝑉= 𝑛𝑅𝑇 𝑃

19. Ideal Gas Law
𝑃𝑉=𝑛𝑅𝑇
𝑛 𝑉 = 𝑃 𝑅𝑇
𝑛𝑀 𝑉 = 𝑃𝑀 𝑅𝑇

20. Ideal Gas Law
𝑛𝑀 𝑉 = 𝑃𝑀 𝑅𝑇
𝑚 𝑉 = 𝑃𝑀 𝑅𝑇
𝐷= 𝑃𝑀 𝑅𝑇

21. Ideal Gas Law
𝐷= 𝑃𝑀 𝑅𝑇
𝑀= 𝐷𝑅𝑇 𝑃 = 𝑚𝑅𝑇 𝑃𝑉

23. Gaseous Mixtures What is the composition of the air that you breathe?
Does air behave like an ideal gas?
Does the size of the gas molecules affect the volume of an Ideal gas?
Is there a factor in the Ideal Gas Law to account for different amounts of gas in a mixture?

24. Dalton’s Law Mole Fraction (XA) Partial Pressure (PA)
Amount of one gas compared to total sample of gas
Partial Pressure (PA)
Pressure exerted by one gas in a sample of gas

25. Dalton’s Law of Partial Pressures
How does partial pressure relate to total pressure?
Sum of partial pressures equals total pressure
PT = PA + PB + PC…

26. Dalton’s Law of Partial Pressures
How can we relate mole fraction to partial pressure and total pressure?

27. In Class Practice
#61, 63, 65, 69 from Ch 10

29. Question Which balloons are better for birthday parties?
Latex or Mylar
Which balloons stay inflated longer?
Why?

30. Temperature Average Kinetic Energy
A gas at any given temperature will have molecules with a wide range of speeds
Range of speeds is calculated by a Maxwell-Boltzman distribution

31. Maxwell-Boltzmann Dist.

32. Molecular speed Root Mean Square velocity
Speed of molecule with average kinetic energy

33. Root Mean Square velocity
As molar mass increases, rms velocity decreases
Remember:
𝑢= 3𝑅𝑇 𝑀
𝐾𝐸= 1 2 𝑚 𝑣 2

34. Root Mean Square velocity

35. Molecular Movement Diffusion Effusion
Movement of molecules throughout a space or throughout a second substance
Effusion
Process in which a gas escapes through a tiny hole in a container

36. Graham’s Law of Effusion
Relates the rate of effusion of two gases
𝑟=𝑢= 3𝑅𝑇 𝑀
𝑟 1 𝑟 2 = 3𝑅𝑇/ 𝑀 𝑅𝑇/ 𝑀 2 = 𝑀 2 𝑀 1

37. Graham’s Law of Effusion
𝑟 1 𝑟 2 = 𝑀 2 𝑀 1
Gases with lower molar masses will effuse faster
Gases with higher molar masses will effuse slower

39. Kinetic Molecular Theory
The particles in a gas are constantly moving in rapid, random, straight-line motion.
Gas particles have no volume compared to the volume of the gas.
No attraction between particles
All collisions are completely elastic

40. Real Gases When do real gases behave more like an Ideal Gas?
High Temperature
Low Pressure
When do real gases behave least like an Ideal Gas?
Low Temperature
High Pressure

41. Real Gases
Why don’t real gases act like ideal gases at low temp and high pressures?
What assumptions of the KMT are no longer accurate?

42. 𝑃+ 𝑛 2 𝑎 𝑉 2 Real Gases Real gases do have attractions
Real gases exert less pressure due to attractions between molecules
a – constant unique to each substance
𝑃+ 𝑛 2 𝑎 𝑉 2

43. 𝑉−𝑛𝑏 Real Gases Real gases do have volume
The amount of free space that molecules actually have is less than an ideal gas
b – constant unique to each substance
𝑉−𝑛𝑏

44. van der Waals Equation
𝑃+ 𝑛 2 𝑎 𝑉 2 𝑉−𝑛𝑏 =𝑛𝑅𝑇

45. van der Waals Equation
𝑃+ 𝑛 2 𝑎 𝑉 2 𝑉−𝑛𝑏 =𝑛𝑅𝑇