# 1.2.7 Practice - Intermolecular forces and the Properties of Gases.docx

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1.2.7 Practice: Intermolecular Forces and the Properties of Gases AP Chemistry Sem 2 Name: Kayla James 1. A spaceship is found to have a tiny leak that allows the effusion of air into space. Air in the spaceship is a mixture of nitrogen (N 2 ), oxygen (O 2 ), argon (Ar), and trace amounts of other gases. a. Predict which of the three main gases will have the lowest rate of effusion and which will have the highest rate. Explain your answer. (1 point) The effusion rate can be estimated according to Graham's law, which states that the effusion rate of a gas is inversely proportional to the square roots of its respective molar masses. According to this, the gas with the highest effusion speed will be the gas with the lowest molar mass, that is, N2. And the one with the lowest effusion speed will be the one with the highest molar mass, that is, Argon. b. Predict how the percentages of the gases in the air will change over time. (1 point) As time passes, the composition of the air will be approximately 21% oxygen, 78% nitrogen, and 0.93% argon. c. Argon is found to effuse through the hole at a rate of 1.6 × 10 –3 mol in 215 s. How much O 2 would effuse through the hole in the same amount of time? (2 points) V Ar = 1.6x10 -3 mol/ 215 s= 7.4x10 -6 mol/s V Ar /V O2 =(M O2 /M Ar ) 1/2 =(32/40) 1/2 V Ar /V O2 = 0.89 V O2 =V Ar / 0.89 = 7.4x10 -6 mol/s / 0.89 = 8.31x10 -6 mol/s n O2 = 8.31x10 -6 mol/s * 215 s = 1.79x10 -3 mol
d. Suppose the three gases were placed at 1.00 atm and 273 K in closed containers, as shown below. A tiny hole is opened in each container, allowing each gas to diffuse into another container filled with neon gas. What is the ratio of the rate of diffusion of nitrogen to the rate of diffusion of oxygen? Is this greater than, less than, or the same as the ratio of the rates of effusion for the two gases? (2 points)
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