Presentation on theme: "Molecular Compostion of Gases"— Presentation transcript:
1Molecular Compostion of Gases Effusion and Diffusion
2Objectives State graham’s law of effusion Determine the relative rate of effusion of two gases of known molar masses.
3Effusion and Diffusion Diffusion – mixing of particles as a result of random motion. Effusion – process by which gas particles pass through a tiny opening.
4Graham’s Law of Effusion The rates of diffusion and effusion depend on the velocity of gas particles.Velocity of gas particles varies inversely with massFor two different gas samples at the same temperature, particles of each gas have the same average kinetic energy. Therefore:
5Graham’s Law of Effusion Multiplying both sides by two and considering that mass is proportional to Molar mass….or…
6Graham’s Law of Effusion The rates of effusion of gases at the same temperature and pressure are inversely proportional to the square roots of their molar masses.Graham's Law Demonstration - Animated - YouTubeBecause the rate of effusion is directly proportional to molecular velocities:Also:
7Sample ProblemsAt 25oC, the average velocity of oxygen molecules is 420 m/s. What is the average velocity of helium atoms at the same temperature?At a certain temperature, hydrogen molecules move at an average velocity of 1.84 x 103 m/s. Estimate the molar mass of a gas whose molecules have an average velocity of 312 m/s.
8Sample ProblemsNitrogen effuses through a pinhole 1.7 times as fast as another gaseous element at the same conditions. Estimate the other element’s molar mass, and determine its probable identity.Determine the molecular mass ratio of two gases whose rates of diffusion have a ratio of 16:1.
9Review QuestionsWhen a cylinder of oxygen is left standing in the sun, the temperature of the gas reaches 42oC. The cylinder has a volume of 10.0 L and contains 128 g of oxygen. What is the pressure in atmospheres inside the cylinder? 10.3 atmSulfur dioxide has a density of g/L at STP. What is its density at a pressure of 108 kPa and 50.0oC? g/LWhat would be the density of 1.0 L of hydrogen at STP? What would be the density of 1.0 L of oxygen at STP?0.089 g/L and 1.4 g/LAn unknown gas effuses at times the effusion rate of nitrogen dioxide. Estimate the molar mass of the unknown gas. 64 g/mol
10Review QuestionsA gas sample that has a mass of g occupies L. Given that the temperature is 281 K and the pressure is 1.44 atm, what is the molar mass of the gas? 27.9 g/molThe density of a gas is 3.07 g/L at STP. Calculate the gas’s molar mass g/molCompare the rates of diffusion of carbon monoxide and sulfur trioxide. CO is 1.7 times faster than SO3