UNIT 7 Exam Review – Gases and Their Properties
Format: 16 multiple-choice questions (32 pts.), 6 calculation problems - 2 of which are multi-part and 1 includes a short written explanation (38 pts.). Be sure you are prepared for the following:
· Define pressure and the effect of changing force and/or area (volume)
· Convert between various units of pressure including mmHg; Torr; atmospheres; and kPa
· Use Boyle’s, Charles, Gay-Lussac’s or the combined gas law to solve for values of pressure, temperature, or volume of a gas
· Use Avogadro’s principle and the ideal gas law to solve for values of volume, pressure, temperature, moles or mass of gas
· Use experimental values of gas density to determine molar mass of a gas
· Use values for gas properties to determine stoichiometric values for reactions involving gases (there are definitely problems involving stoichiometry calcs and potentially even limiting reagent and excess remaining calcs)
· Use the Kinetic Molecular Theory to explain the motion/behavior of gas particles and the properties of gaseous substances (be sure to be familiar w/ each of the postulates)
· Use the Maxwell-Boltzmann distribution curve to describe the relationship between gas temperature and particle motion. Be able to compare curves of different gases at the same temp., or the same gas at different temps.
· Use Dalton’s law of partial pressures to determine partial pressures for gases in a mixture and to correct values for gases collected over water
· Use Graham’s Law to compare effusion/diffusion rates of gases and to calculate rates of effusion and molecular/molar masses
· Compare the behavior of ideal and real gases, explain the conditions under which gases are most ideal and which of a group of gases would most deviate from the ideal gas law
· Use the van der Waals equation to predict the effect on gas volume and pressure under conditions of increasing pressure and decreasing temperature
XClO3 (s) → XCl(s) + 3/2 O2 (g)
The equation above represents the decomposition of a compound containing an unknown element, X. A 1.39 g sample of XClO3 (s) was completely decomposed by heating. The gas produced by the reaction was captured over water in a gas-collection tube at 24.0 0C. The total volume of gas in the tube was 506 mL, and the total pressure inside the tube was determined to be 739.5 torr. The vapor pressure of water is 22.4 torr at 24.0 0C.
(a) Calculate the partial pressure, in Torr, of the O2 (g) that was collected at 24.0°C.
(b) Calculate the number of moles of O2 (g) collected at 24.0°C.
(c) Determine the number of moles of XClO3 (s) that decomposed.
(d) Determine the molar mass of the compound.
(e) Determine the identity of element X.
The experimental apparatus represented above is used to demonstrate the rates at which gases
diffuse. When the cotton balls are placed in the ends of a tube at the same time, the gases diffuse
from each end and meet somewhere in between, where they react to form a white solid. Which of
the following combinations will produce a solid closest to the center of the tube?
(A) HCl and CH3NH2 (B) HCl and NH3 (C) HBr and CH3NH2 (D) HBr and NH3
In which flask do the molecules have the greatest average speed?
Which flask contains the smallest number of moles of gas?
Which flask contains the sample with the greatest density?