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Gases as a Form of Matter

Gases as a Form of Matter. Unit 2, Week 2. Kinetic Molecular Theory and Gases. Remember Kinetic Molecular Theory?. Assumptions of KMT for Gases. In regards to gases, there are 3 basic assumptions. Entities mean “atoms or molecules”

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Gases as a Form of Matter

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  1. Gases as a Form of Matter Unit 2, Week 2

  2. Kinetic Molecular Theory and Gases Remember Kinetic Molecular Theory?

  3. Assumptions of KMT for Gases In regards to gases, there are 3 basic assumptions. Entities mean “atoms or molecules” • 1. Gas entities are separated by LARGE, EMPTY spaces. ∴ gases are COMPRESSIBLE. There are NO attractive or repulsive forces between gas entities.

  4. 2. Gas entities are always MOVING and moving FAST! ∴ gases fill up the volume of their container and put pressure on the walls of their container. • 3. Collisions between gas entities are ELASTIC, meaning ALL the energy is transferred from one entity to another during a collision.

  5. Sketch a picture of how gas particles would fill a beaker by thinking about the 3 assumptions of Kinetic Molecular Theory:

  6. Kinetic Energy and Temperature • Kinetic energy is the energy of motion. • Temperature is a measure of the average kinetic energy of all the entities of a substance. • We can measure the increase/decrease in average kinetic energy by measuring the temperature change.

  7. Kelvin Scale (Temperature) • There is an absolute lower limit. • The temperature at which the motion of the particles STOPS is known as absolute zero. • Absolute zero is -273.15°C. • Zero Kelvin (0K) is -273.15°C. Why is the Kelvin scale useful then?

  8. Celsius vs. Kelvin Note: there is no degree symbol used for Kelvin

  9. Converting: • Celsius to Kelvin • Add 273.15 • Ex: Convert 37°C to K. • 37 + 273.15 = 310.15K • Kelvin to Celsius • Subtract 273.15 • Ex: Convert 250K to °C • 250 - 273.15 = -23.15°C

  10. KMT and Pressure Pressure is a force exerted over an area. • Write the equation to show the inverse relationship between P, F and A. Think: What is gas pressure caused by? Larger area, fewer collisions Smaller area, more collisions

  11. KMT and Pressure When no gas entities are present, no collisions or pressure exists, we call this empty motionless space a ____________.

  12. Think: Can you explain what atmospheric pressure or air pressure is then? How do we measure air pressure? Barometer. Think: When working with gases we need to set standard conditions. Can you reason why? • Standard temperature and pressure (STP): 0°C and 101.325kPa. • Standard ambient temperature and pressure (SATP): 25°C and 100kPa. This is much more reasonable for lab work!

  13. Crush me if you can!

  14. Air & Air Pressure

  15. Pressure Units • Pressure can be measured in three units: • kPa (kiloPascals) - this is the SI unit • mmHg (millimetres of mercury) • atm (atmospheres) • Conversion factor: • 1 atm = 760 mmHg = 101.325 kPa

  16. Activity • Complete the table below: (remember 1atm = 101.325kPa = 760mmHg)

  17. Boyle’s Law: Relationship between P and V • According to Boyle’s Law, for a gas with a constant mass and temperature, there is an inverse relationship between pressure and volume. Sketch the graphing relationship:

  18. For any inverse relationship the product of the two quantities is always equal to a constant (k). P1 P2 P3 Equilibrium V1 V2 V3 P1 = 10 kPa V1 = 10 L P1V1 = 100 kPa ●L P2 = 5 kPa V2 = 20 L P2V2 = 100 kPa ● L P3 = 20 kPa V3 = 5 L P3V3 = 100 kPa ● L Note that in each case PxVx remains constant!!

  19. Boyle’s Law Animation http://www.grc.nasa.gov/WWW/K-12/airplane/aboyle.html

  20. Boyle’s Law • Boyle’s Law can be written mathematically as: • P1V1 = P2V2 • What 2 things need to be constant for Boyle’s Law to hold true? (assumptions) • Temperature (T) • # of gas molecules (you can think of it as mass).

  21. Examples Ex 1: If the pressure of 2.50L of anesthetic gas changes from 100kPa to 40kPa, what will be the new volume of the gas? (Assume the T remains constant.)

  22. Ex 2: If the volume of a 50kPa cylinder changes from 75L to 125L, what is the new pressure within the cylinder? (Assume the T remains constant.)

  23. Practice Booklet: 15 mins • Complete Boyle’s Law Questions, p. 1 • What you don’t finish is for homework

  24. Charles’ Law: Relationship between T and V http://youtu.be/IkRIKGN3i0k

  25. Charles’ Law: Relationship between T and V • According to Charles’ Law, for a gas with a constant mass and pressure, there is a direct relationship between temperature and volume. • Sketch the graphing relationship below:

  26. Charles’ Law: Relationship between T and V • Charles’ Law is therefore written as: • What 2 things need to be constant for Charles’ Law to hold true? • Pressure (P) • # of gas molecules (you can think of it as mass) V1 = V2 T1 T2

  27. In any direct relationship, the ratio of the two quantities that change is a constant (k). 100kPa 100kPa V2 = 2L V1 = 1L T1= 300K T2= 600K V1 = 2L T1 = 600K k=V1 T1 k= 2L 600K k= 0.003L/K V1 = 1L T1 = 300K k =V1 T1 k= 1L 300K k= 0.003L/K

  28. Ex 1: What will be the volume of a gas at 27°C, if its volume at 32.7°C is 6.8L? (Assume P and amount of gas are constant. Remember T must be in K.)

  29. Ex 2: What is the temperature of a gas at 5.0L, if its temperature at 25.5°C is 9.5L? (Assume P and amount of gas are constant. Remember T must be in K.)

  30. Practice Booklet: 15 mins • Complete Charles’ Law Questions, p. 2 • What you don’t finish is for homework

  31. The Combined Gas Law • The Combined Gas Law shows the relationship that exists between volume, temperatureand pressure for any fixed amount of a gas. Think: Can you guess what the formula looks like? P1V1 = P2V2 T1 T2

  32. Boyle’s Law can be derived by holding temperature constant: P1V1 = P2V2 T1 T2 P1V1 = P2V2 T1 T2 If T1=T2 then: ∴ , P1V1 = P2V2

  33. Charles’ Law can be derived by holding pressureconstant: P1V1 = P2V2 T1 T2 P1V1 = P2V2 T1 T2 If P1=P2 then: ∴ , V1 = V2 T1 T2

  34. Ex 1: A 450mL sample of Freon at 1.50atm and 15⁰C was compressed to 300mL when a pressure of 2.00atm was exerted. Calculate the final temperature in degrees Celsius. (Answer: -17C)

  35. Ex 2: A 2.75L sample of helium gas at 99.0kPa was heated from 21.0oC to 71.0oC and the pressure was changed to 100kPa. Calculate the final volume. (Answer: 3.19L)

  36. Practice Booklet: 15 mins • Complete Combined Gas Law Questions, p. 3-4 • What you don’t finish is for homework

  37. What are Moles?

  38. Law of Combining Volumes In 1809, Joseph Gay-Lussac derived the Law of Combining Volumes: • The volumes of gases in chemical reactions are always in whole number ratios. Ex: Reaction of hydrogen gas and chlorine gas at the same temperature and pressure. • H2(g) + Cl2(g) = 2HCl(g) Volume: 1.0L 1.0L 2.0L Ratio: 1 1 2

  39. Avogadro’s Theory In 1811, Avogadro proposed an explanation for the law of combining volumes: • Equal volumes of gases at the same pressure and temperature contain an equal # of molecules. • This means that the volume of gas is directly proportional to the number of moles of the gas present. • Ex: Coefficients: 2C8H18(g) + 25O2(g) --> 16CO2(g) + 18H2O(g) Mole Ratio: 2mol 25mol 16mol 18mol Volume Ratio: 2L 25L 16L 18L

  40. NOTE: Volume is NOT conserved. • But, we can use the mole ratio to make predictions about the volumes of other entities. Ex: Predict the volume of oxygen required to burn 120mL of octane (C8H18(g)). Video: Rock Me Avogadro!

  41. Ex 1: Gas barbecues burn propane (C3H8(g)) using oxygen from the air in a combustion reaction. If 5.00L of propane is burned, predict the volume of oxygen required for complete combustion. (Assume same T & P.) (Answer: 25.0L)

  42. Ex 2: Cars contain a catalytic converter which converts nitrogen monoxide (a pollutant) into nitrogen and water vapour by reacting with hydrogen. The catalytic converter removes about 1.2L of nitrogen monoxide at SATP for every kilometer of driving. What volume of nitrogen gas is formed at the same T & P? (Answer: 0.60L)

  43. Ex 3: Ammonia (NH3(g)) is produced from its elements in huge quantities. Predict the volume of hydrogen gas required to produce 1.0ML of ammonia, assuming the same T & P. (FYI: 1ML = 1.0 x 106L) (Answer: 1.5ML)

  44. Practice Booklet: 15 mins • Complete Molar Volume Questions, p. 5-6 • What you don’t finish is for homework

  45. The Ideal Gas Law The molecules and atoms of an ideal gas: • Take up little volume • Have no attractive forces. • Behave perfectly under all conditions of T, P and V. Think: Does this exist in reality?

  46. Ideal vs. Real Gases

  47. As a simplification, it is valid to assume that most real gases behave as ideal gases IF low pressuresandhigh temperatures(such as those at STP and SATP) are maintained.

  48. The Ideal Gas Law • Most commonly it is written as: PV = nRT • This law can be stated as

  49. Ex 1: How many grams of air are contained in a child’s lungs which have a capacity of 2.2L? Air pressure is 100kPa, body temperature is 37°C and we can assume the molar mass of air is 29.00g/mol. (Answer: 2.5g)

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