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Understanding Gases: Kinetic-Molecular Theory and Gas Laws

This study guide delves into the properties and behavior of gases through the lens of the kinetic-molecular theory. It covers essential concepts such as temperature, pressure, diffusion, effusion, and the interrelationships among pressure, volume, and temperature. Key laws, including Boyle's, Charles's, and Dalton's law of partial pressures, are explained with real-world applications and calculations. Ideal gas behavior is discussed along with problem-solving strategies to predict and analyze gases' behavior under different conditions. Ideal for chemistry students looking to master gas concepts.

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Understanding Gases: Kinetic-Molecular Theory and Gas Laws

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  1. Turn in your Homework

  2. Gases Chapters 12.1 and 13

  3. Gases Chemistry- Matter and Change: 12.1

  4. 12.1 Main Idea Gases expand, diffuse, exert pressure, and can be compressed because they are in a low-density state consisting of tiny, constantly moving particles

  5. Objectives • Predict the behavior of gases using the kinetic-molecular theory • Explain how mass affects the rates of diffusion and effusion • Measure gas pressure • Calculate effusion rates

  6. Review Vocabulary • Kinetic energy • Molar mass

  7. New Vocabulary • Kinetic-molecular theory • Elastic collision • Temperature • Diffusion • Graham’s Law • Pressure • Barometer • Manometer • Pascal (Pa) • Atmosphere (atm)

  8. Kinetic Energy • The energy an object has because of its motion is called kinetic energy. • According to the kinetic theory, all matter consists of tiny particles that are in constant motion.

  9. Kinetic-Molecular (KM) Theory • Assumptions • Particle size is very small • Particles take up relatively no space • Particles are far apart • Very little interaction of particles • Collisions are elastic • No kinetic energy is lost in a collision

  10. Gases are in constant rapid motion.

  11. Gas particles travel in straight line paths.

  12. Behavior of Gases: Temperature • Determined by mass and velocity • Temperature- the average kinetic energy of particles in matter

  13. Absolute zero • Theoretical point at which all molecular motion stops. • 0 K; -273.15 °C; −459.67° F

  14. Kinetic Energy and Temperature

  15. Behavior of Gases: Pressure • Pressure- the result of simultaneous collisions of billions of rapidly moving particles in a gas with an object.

  16. Pressure • Pressure (P) is defined as the force per unit area on a surface. (P=F/A) • Gas pressure is caused by collisions of the gas molecules with each other and with surfaces with which they come into contact. • The pressure exerted by a gas depends on volume, temperature, and the number of molecules present. • The greater the number of collisions of gas molecules, the higher the pressure will be.

  17. Gas Pressure • Units • Pascal (1 Pa = N /m2) • *Atmosphere (1 atm = 101.3 kPa) • *mm Hg (1 atm = 760 mm Hg) • *Torr (1 torr = 1 mm Hg)

  18. Gas Pressure Barometer Manometer Manometers measure gas pressure in a closed system • Barometers measure atmospheric pressure • open system

  19. Atmospheric air pressure changes with altitude and weather

  20. Behavior of Gases: Volume • Compression and expansion- density of material can be changed by changing the available volume

  21. Behavior of Gases: Motion • Diffusion- movement of one material through another • Concentration gradient • Effusion- gas escaping from a confined space through tiny openings

  22. What is the ratio of the rate of diffusion for ammonia and hydrogen chloride?

  23. Calculate the ratio of effusion rates for nitrogen gas and neon • RN/RNe=0.849

  24. Can you… • Predict the behavior of gases using the kinetic-molecular theory • Explain how mass affects the rates of diffusion and effusion • Measure gas pressure

  25. Homework • Packet pg 3-4 and 10 • Textbook pg 405 (1-3) pg 409 (4-7)

  26. The Gas Laws Chapter 13.1

  27. 13.1 Main Idea For a fixed amount of gas, a change in one variable- pressure, volume or temperature- affects the other two.

  28. 13.1 Objectives • Calculate the partial pressure of a gas • State the relationships among pressure, volume, temperature, and the amount of gas • Apply gas laws to problems involving pressure, volume, temperature, and the amount of gas • Create graphs of the relationships among pressure, volume, temperature, and the amount of gas • Solve problems related to fixed amounts of gases

  29. Review Vocabulary • Scientific law • Directly related • Indirectly (inversely) related • Kelvin

  30. New Vocabulary • Ideal gas • Absolute zero • Dalton's law of partial pressure • Boyle’s law • Charles’s law • Gay-Lussac’s law • Combined gas law

  31. Dalton’s Law of Partial Pressures • total pressure is the sum of the partial pressures • Ptot=P1 + P2 + P3 + … Pn

  32. A mixture of O2, CO2 and N2 has a total pressure of 0.97 atm. What is the partial pressure of O2 if the partial pressure of CO2 is 0.70 atm and the partial pressure of N2 is 0.12 atm? • 0.97 atm = 0.70 atm + 0.12 atm + x • X = 0.15 atm

  33. Ideal gases • Non-existent, but assumes the following: • Completely elastic collisions • Particles occupy no volume • Large number of particles • No attractive or repellent forces between particles • Molecules are in completely random motion

  34. Boyle’s Law • Constants: amount of gas (n) and temperature (T) • Boyle's Law in Motion

  35. A diver blows a 0.75 L air bubble 10 m under water. As it rises, the pressure goes from 2.25 atm to 1.03 atm. What is the volume of the bubble at the surface? • P1V1=P2V2 2.25 atm 0.75 L = 1.6 L 1.03 atm

  36. A sample of oxygen gas has a volume of 150.0 mL when its pressure is 0.947 atm. What will the volume of the gas be at a pressure of 0.987 atm if the temperature remains constant? • Given:V1 of O2 = 150.0 mL • P1 of O2 = 0.947 atm • P2of O2= 0.987 atm • Unknown:V2of O2in mL • Solution: • Rearrange the equation for Boyle’s law (P1V1 = P2V2) to obtain V2.

  37. Plug and chug...

  38. Charles’s Law • Constants: amount of gas (n) and pressure (P) • Temperature is in Kelvin (K) • K= C + 273.0 • Charles' Law in Motion

  39. A helium balloon in a closed car occupies a volume or 2.32 L at 40°C.If the temperature rises to 75°C, what is the new volume of the balloon? • V2=V1T2/T1 348.0 K 2.32 L = 2.58 L 313.0 K

  40. A sample of neon gas occupies a volume of 752 mL at 25°C. What volume will the gas occupy at 50°C if the pressure remains constant?

  41. Given:V1 of Ne = 752 mL • T1 of Ne = 25°C + 273 = 298 K • T2of Ne = 50°C + 273 = 323 K • Unknown:V2of Nein mL • Solution: • Rearrange the equation for Charles’s law to obtain V2.

  42. Gay-Lussac’s Law • Constants: amount of gas (n) and volume (V) • T must be in Kelvin • Gay-Lussac in Motion

  43. The pressure of oxygen gas inside a canister is 5.00 atm at 25°C. the canister is placed in a cold environment where the temperature is -10°C; what is the new pressure in the canister? • P2=P1T2/T1 263.0 K 5.00 atm = 4.41 atm 298.0 K

  44. The gas in a container is at a pressure of 3.00 atm at 25°C. Directions on the container warn the user not to keep it in a place where the temperature exceeds 52°C. What would the gas pressure in the container be at 52°C?

  45. Given:P1 of gas = 3.00 atm • T1 of gas = 25°C + 273 = 298 K • T2of gas = 52°C + 273 = 325 K • Unknown:P2of gasin atm • Solution: • Rearrange the equation for Gay-Lussac’s law to obtain P2.

  46. Predict • The relationship between pressure and amount of gas at a fixed temperature and volume • Pressure-Moles relationship • The relationship between volume and the amount of gas at a fixed temperature and amount of gas • Volume-Moles relationship

  47. Combined Gas Law • Combination of Boyle’s, Charles’, and Gay-Lussac’s laws

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