introduction to gases and kinetic molecular theory

intro to gas

1. EQ: How do we use the Kinetic Molecular Theory to explain the behavior of gases? Topic: Introduction to Gases

2. States of Matter 2 main factors determine state: The forces (inter/intramolecular) holding particles together The kinetic energy present (the energy an object possesses due to its motion of the particles) KE tends to ‘pull’ particles apart

3. Kinetic Energy , States of Matter & Temperature Gases have a higher kinetic energy because their particles move a lot more than in a solid or a liquid As the temperature increases, there gas particles move faster, and thus kinetic energy increases.

4. Characteristics of Gases Gases expand to fill any container. random motion, no attraction Gases are fluids (like liquids). no attraction Gases have very low densities. no volume = lots of empty space

5. Characteristics of Gases Gases can be compressed. no volume = lots of empty space Gases undergo diffusion & effusion (across a barrier with small holes). random motion

6. Lesson 1: Kinetic Molecular Theory

7. Discuss the postulates of the Kinetic molecular theory. Explain the properties of gases. Participate actively throughout the discussion

8. Temperature Pressure Spread out Space Amount/Number Force

9. Properties of Gases

10. Fundamental Properties of Gases 1. Volume Symbol: V Unit: mL or L

11. Fundamental Properties of Gases 2. Temperature Symbol: T Unit: °C or K

12. Fundamental Properties of Gases 3. Pressure Symbol: P Unit: 1 Atm = 760 Torr 1 Atm = 101,325 Pa 760 Torr = 760 mmHg 760 mmHg = 1 Atm

13. Fundamental Properties of Gases 4. Amount of gas/Number of Moles Symbol: n Unit: mol

14. How to calculate the amount of gas? Example: How much gas is present in 2g of carbon dioxide? Step 1: Look for the mass given in the problem: CO2 = 2g

15. How to calculate the amount of gas? Step 2: Get the molar mass of each atom (CO2) Element Number of atoms Atomic mass Total C O Molar mass

16. How to calculate the amount of gas? Step 2: Get the molar mass of each atom (CO2) Element Number of atoms Atomic mass Total C 1 12 O 2 16 Molar mass

17. How to calculate the amount of gas? Step 2: Get the molar mass of each atom (CO2) Element Number of atoms Atomic mass Total C 1 O 2 Molar mass

18. How to calculate the amount of gas? Step 2: Get the molar mass of each atom (CO2) Element Number of atoms Atomic mass Total C 1 12 12 O 2 16 Molar mass

19. How to calculate the amount of gas? Step 2: Get the molar mass of each atom (CO2) Element Number of atoms Atomic mass Total C 1 12 12 O 2 16 32 Molar mass

20. How to calculate the amount of gas? Step 2: Get the molar mass of each atom (CO2) Element Number of atoms Atomic mass Total C 1 12 12 O 2 16 32 Molar mass 44

21. How to calculate the amount of gas? Step 3: Divide the mass of gas by the molar mass n = ------------------- 2g 44g/mol 0.05 mol n =

22. Try This! Example: How much gas is present in 200g of water vapor? Step 1: Look for the mass given in the problem: H2O = 200g

23. Other Properties of Gases 5. Compressibility

24. Other Properties of Gases 5. Diffusion vs. Effusion

25. Kinetic Molecular Theory

26. Kinetic Molecular Theory Rudolf Clausius James Clerk Maxwell Ludwig Boltzmann

27. Postulate 1: Particles are in constant random straight motion and will collide against other particles or the container wall Kinetic Molecular Theory

28. Postulate 2: Collision among particles is perfectly elastic Kinetic Molecular Theory

29. Postulate 3: The kinetic energy of molecules is directly proportional to the temperature. Kinetic Molecular Theory

30. Postulate 4: The volume of gas particles is negligible Kinetic Molecular Theory

31. Postulate 5: Attractive or repulsive forces of gas molecules are also negligible Kinetic Molecular Theory

32. Kinetic Molecular Theory of ‘Ideal’ Gases Particles in an ideal gas… have no volume. have elastic collisions (ie. billiard ball🡪 particles exchange energy with eachother, but total KE is conserved are in constant, random, straight-line motion. don’t attract or repel each other. have an avg. KE directly related to temperature ( temp= motion= KE )

33. Real Gases Particles in a REAL gas… have their own volume attract each other (intermolecular forces) Gas behavior is most ideal… at low pressures at high temperatures Why???

34. Real Gases At STP, molecules of gas are moving fast and are very far apart, making their intermolecular forces and volumes insignificant, so assumptions of an ideal gas are valid under normal temp/pressure conditions. BUT… at high pressures : gas molecules are pushed closer together, and their interactions with each other become more significant due to volume at low temperatures : gas molecules move slower due to KE and intermolecular forces are no longer negligible

35. Pressure

36. Atmospheric Pressure The gas molecules in the atmosphere are pulled toward Earth due to gravity, exerting pressure Why do your ears ‘pop’ in an airplane?

37. Pressure Barometer measures atmospheric pressure Mercury Barometer

38. Units of Pressure At Standard Atmospheric Pressure (SAP) 101.325 kPa (kilopascal) 1 atm (atmosphere) 760 mm Hg (millimeter Hg) 760 torr 14.7 psi (pounds per square inch)

39. Standard Temperature & Pressure Standard Temperature & Pressure 0°C 273 K 1 atm 101.325 kPa -OR- STP

40. Temperature: The Kelvin Scale ºC K -273 100 273 373 K = ºC + 273 Always use absolute temperature (Kelvin) when working with gases.

41. Converting between Kelvin and Celsius o C =_____K 100 o C= _____K 25 o C =______K -12 o C = ______K -273K = ______ o C 23.5K = ______ o C 373.2K= ______ o C K = ºC + 273

42. IDENTIFY THE STATE OF MATTER