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Gases

Gases. Chapters 12.1 and 13. Big Idea. Gases respond in predictable ways to pressure, temperature, volume and changes in the number of particles .

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Gases

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  1. Gases Chapters 12.1 and 13

  2. Big Idea Gases respond in predictable ways to pressure, temperature, volume and changes in the number of particles. Gases expand, diffuse, exert pressure, and can be compressed because they are in a low-density state consisting of tiny, constantly moving particles

  3. 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

  4. Vocabulary • Kinetic energy • Molar mass • Kinetic-molecular theory • Elastic collision • Temperature • Pressure • Atmosphere (atm)

  5. 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.

  6. 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

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

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

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

  10. 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. • Compression and expansion- density of material can be changed by changing the available volume

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

  12. 13.1 Main Idea and Objectives • For a fixed amount of gas, a change in one variable- pressure, volume or temperature- affects the other two. • 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

  13. Review Vocabulary • Scientific law • Directly related • Indirectly (inversely) related • Kelvin • Ideal gas • Absolute zero • Dalton's law of partial pressure • Boyle’s law • Charles’s law • Gay-Lussac’s law • Combined gas law

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

  15. 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?

  16. 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

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

  18. 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?

  19. 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?

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

  21. 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?

  22. 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?

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

  24. 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?

  25. 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?

  26. 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

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

  28. A gas at 110 kPa and 30.0°C fills a flexible container with an initial volume of 2.00L. If the temperature is raised to 80.0°C and the pressure increases to 440 kPa, what is the new volume?

  29. Gas Law Summary

  30. 13.2 Main Idea and Objectives • The ideal gas law relates the number of particles to pressure, temperature, and volume • Relate the amount of gas present to its pressure, temperature, and volume using the ideal gas law • Compareandcontrast the properties of real gases and ideal gases • Solve problems using the ideal gas law

  31. Vocabulary • Mole • STP • Avogadro’s principle • Molar volume • Ideal gas constant (R) • Ideal gas law

  32. STP • Standard temperature and pressure • Standard temperature • 0.00000°C = 273.15 K • Standard pressure • 1 atm = 760 torr = 101.325 kPa

  33. Ideal Gas Law • PV=nRT • P = pressure (atm) • V = volume (L) • n = number of moles of gas (mol) • R = gas constant (L•atm)/(mol•K) • T = temperature (K)

  34. Calculate the number of moles of ammonia gas contained in a 3.0 L vessel at 300 K with a pressure of 1.50 atm.

  35. Ideal gas and Real gases Ideal gas Real gas Particles occupy volume KE is lost during collisions Limited numbers of molecules Inter-molecular forces exist • Particles occupy no volume • All collisions are perfectly elastic • Infinitely large number of molecules • No forces between molecules

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