# Gases have different physical and chemical properties

Unit H Review—The Behavior of GasesSummaryGases have different physical and chemical properties. All gases have properties that can be explained by theIdeal Gas Model of the Kinetic Molecular Theory. This theory states: Gas molecules have no volume comparedto the total space they occupy. There are no attractions between gas molecules. Gas molecules are constantlymoving and colliding. All gas molecules have the same average kinetic energy (AKE) at the same temperature. Gas pressure is a result of moving gas molecules colliding with the walls of the container. Such pressurecan be measured using pressure gauges and pressure sensors. Air pressure, specifically, is measured with abarometer. The gas laws are a series of mathematical equations, in agreement with the Ideal Gas Model, that can beused to make predictions of pressure, volume, temperature, and moles of molecules. Real gases do behave very closely (within a few percent) of what the Ideal Gas Model predicts attemperatures and pressures normally encountered in a typical high school laboratory. At low temperatures andhigh pressures, however, real gases can be made to condense to liquids. This is because real gas molecules dooccupy some space and do have some attraction for each other. The nature of these attractions forms a majorportion of the content of the next unit. Gas LawBoyle’sCharles’CombinedEquationP1V1 = P2V2V1 = V2T1 T2P1V1 = P2V2T1T2Gas Law(at constant T and n)Avogadro’s(at constant P and n)Ideal(at constant n)Dalton’sEquationV1 = V2n1n2PV = nRT(at constant P and T)(R = 8. 314 kPaL mol-1 · K-1)Ptotal = P1 + P2 + P3 + …Review Questions: Multiple-Choice: 1. Which pressure is different from the others?A. 790 mmHgB. 105 kPaC. 1. 04 atmD. Choices A, B, and C are all the same pressure. 2. As the temperature of a gas increases, the kinetic energy of its particlesA. increases. B. decreases. C. remains the same. 3. If the volume of a balloon expands, and the temperature remains constant, the pressure on the balloonA. increases. B. decreases. C. remains the same. 4. If the temperature of the air inside an automobile tire increases, but the tire does not expand, the pressureof the air inside the tireA. increases. B. decreases. C. remains the same. 5. A partially inflated weather balloon is released. If the air temperature is constant, but the air pressurearound the balloon drops as the balloon rises, the volume of the weather balloonA. increases. B. decreases. C. remains the same. 6. A chemist has a certain volume of gas in a balloon. If the volume of gas decreases overnight, but thepressure remains constant, the temperature of the gasA. increases. B. decreases. C. remains the same. 7. All gases deviate from ideal gas behavior, particularly at high pressures and lowtemperatures. A. TrueB. False8. Temperatures below absolute zero are not possible. A. TrueB. FalseP9. For an ideal gas V is a constant. A. TrueB. False10. In a mixture of gases, each gas behaves independently of the other gases in the mixture. A. TrueB. False11. Which temperature scale provides a direct measure of the average kinetic energy of a substance?A. CelsiusB. KelvinC. FahrenheitD. Reamur12. What is the name of a device used to measure gas pressure?A. ThermometerB. VaporometerC. CalorimeterD. Barometer13. Which law describes the relationship between the volume and temperature of a gas?A. Boyle’s LawB. Dalton’s LawC. Charles’ LawD. Gay-Lussac’s Law14. According to Avogadro’s Principle, equal ____ of gas at the same temperature and pressure contain equalnumbers of particles. A. massesB. volumesC. samplesD. areas15. The individual molecules of gas at STPA. never collide. B. all have the same speed. C. travel at different speeds. D. have a constant speed. 16. If kinetic energy is added to a sample of gas in a rigid container, which of the following takes place?A. The temperature increases. B. The pressure increases. C. The molecules of gas move faster. D. All the above occur. 17. If two different gases have the same kinetic energy,A. the gas with more mass has a greater velocity. B. the gas with more mass has a lower velocity. C. the gases have the same velocity, regardless of mass. D. the gas with more mass has a higher temperature. 18. Gases deviate from ideal behavior because gas particlesA. are in continuous motion. B. move randomly in straight lines. C. have different amounts of kinetic energy. D. have some attraction for each other. 19. When a closed tank of air is heated, the density of the air (neglecting any expansion of the tank)A. increases. B. decreases. C. remains the same. 20. Which of the following is NOT one of the postulates of the Kinetic-Molecular Theory of gases?A. Gas molecules are in a state of constant, random motion. B. The diameter of a gas molecule is large when compared with the distance between gasmolecules. C. There is no force of attraction between gas molecules. D. The temperature of a gas is a reflection of the average kinetic energy of the gas. E. Choices A, B, C, and D are all postulates of the Kinetic-Molecular Theory. Problems: 21. 59. 7 cm3 of helium gas at 95. 0 kPa is expanded to 100. 0 cm3 at constant temperature. What is the newpressure on the gas?22. Oxygen gas is collected over water at a temperature of 25. 0C and a pressure of 746. 8 mmHg. What isthe pressure due to dry oxygen gas?23. What pressure will be exerted by 7. 99 g of butane, C4H10, if the gas is in a container measuring 1. 50 L andis at 27C?24. 5. 18 L of nitrogen gas at 76. 0C are cooled to 6. 0C at constant pressure. Calculate the new volume of thegas. 25. What is the molar mass of a gas if 372. 0 mL has a mass of 0. 800 g at 99. 8C and 106. 6 kPa?26. What volume of CO2(g) is produced when 1. 05 kg of ethane, C2H6(g), is burned? The temperature is24. 0C and the pressure is 745. 0 mmHg. 2 C2H6(g) + 7 O2(g)4 CO2(g) + 6 H2O(g)Unit I Review—Liquids, Solids and Phase Changes (optional material in red)Summary: There are not only intermolecular attractions between molecules in the gas phase, but those forces of attractionare extremely important for liquids and solids. The Kinetic-Molecular Theory is fundamental to the understanding of matter. The Kelvin temperaturescale is an indicator of relative molecular motions, with the particles having no motion at absolute zero. Intermolecular forces are called van der Waals forces: London dispersion forces and dipole-dipole forces. Aspecial case of dipole-dipole forces is hydrogen bonding, which have higher than expected melting and boilingpoints, enhanced solubility, unique molecular shapes, etc. Ionic bonding is the result of a 3-dimensional array of positive and negative ions attracting each other,resulting in very high melting and boiling points. Metallic bonding occurs because the valence electrons in metal atoms are free to move to any of theempty orbitals in the crystal and, therefore, belong to the whole crystal rather than just between two atoms. Substances that have network covalent bonding are generally very hard, strong, brittle, and have extremely highmelting and boiling points. Most do not conduct electricity. In order to undergo a phase change, the attractions between whole particles (atoms, ions, or molecules)in the substance must overcome interparticle attractions (van der Waals, metallic bonds, ionic bonds or covalentbonds). Vocabulary: absolute zerodepositionhydrogen bondintermolecular forceslattice energyLondon dispersion forcesvan der Waals forcesvapordipole-dipole forceshydrogen bondinterparticle attractionsisoelectronicnormal boiling pointsublimationvapor pressurevaporizationReview Questions: Multiple-Choice: 1. Substances that are liquids at room temperature or below areA. ionic. B. nonpolar covalent molecular. C. metallic. D. covalent network. 2. Crystals such as diamonds (very hard, high melting point, nonconductors) are classified asA. ionic crystals. B. covalent molecular crystals. C. covalent network crystals. D. metallic crystals. 3. Metallic crystals characteristically haveA. good electric conductivity. B. great hardness. C. low melting points. D. brittleness. 4. Because of the hydrogen bonds in water, the hydrogen atom of one water molecule may beA. weakly attracted to the oxygen of a second water molecule. B. weakly attracted to the hydrogen of a second water molecule. C. strongly attracted to the second hydrogen of its own molecule. D. strongly attracted to the oxygen of a second water molecule. 5. As ice is heated from a lower temperature towards its melting point, the hydrogen bondsA. get stronger. B. stretch. C. increase in number. D. cause the formation of hexagonal patterns. 6. What is thought to cause dispersion forces?A. attraction between ionsB. motion of electronsC. differences in electronegativityD. the formation of hexagonal patterns7. Why is hydrogen bonding only possible with hydrogen?A. because hydrogen is the only atom whose nucleus is not shielded by electrons when it isinvolved in a covalent bondB. because hydrogen is the only atom that is the same size as an oxygen atomC. because hydrogen has the highest electronegativity of any element in the periodic table8. What is the basis of a metallic bond?A. the attraction of metal ions for mobile electronsB. the attraction between neutral metal atomsC. the neutralization of protons by electronsD. the attraction of oppositely charged ions9. What occurs during the dissolving of an ionic crystal?A. Ions separate from molecules. B. Molecules surround ions. C. Molecules bind covalently to molecules. D. Ionic compounds are formed. 10. Why are two nonpolar substances able to dissolve each other?A. There is no repulsive force between them. B. They combine to produce a polar substance. C. There is no attractive force between them. D. Nonpolar molecules cannot dissolve in each other. 11. Chlorine is a gas, bromine is a liquid, and iodine a solid because of differences in the strength of theirA. hydrogen bonds. B. dispersion forces. C. dipole interactions. D. polar bonds. 12. The high surface tension of water is due to theA. small size of water molecules. B. high kinetic energy of water molecules. C. hydrogen bonding between water molecules. D. covalent bonds in water molecules. 13. It has been said, “There are forces of attraction between molecules in all chemical systems. ” Which of thefollowing experimental observations supports this statement?A. Gases can be condensed to form liquids. B. Solids are very difficult to compress. C. Liquids have an indefinite shape. D. Not all solids are ionic crystals. 14. Ionic solidsA. are soft and have low melting points. B. melt to form liquids that conduct electricity. C. are malleable. D. conduct electricity. 15. Solid sodium metal and molten sodium chloride conduct electricity because both containA. mobile electrons. B. mobile ions. C. active metals, which are good conductors. D. mobile charged particles. For questions #16 to 26, write the letter of the bond or attractive force, chosen from the list below, thatis most closely associated with that compound or phrase. A. ionic bondE. metallic bondB. network covalent bondsF. covalent bondsC. dipole-dipole attractionsG. dispersion forcesD. hydrogen bonds16. Are weak enough to permit solid iodine to sublime readily upon heating. 17. Al(s)18. Bond noble gas atoms in the liquid phase. 19. Responsible for the extremely high melting point of diamond (above 3500º C). 20. Link the atoms in a molecule of a diatomic gaseous element. 21. Allows methanol to be infinitely soluble in ethanol. 22. SiO2(s)23. Positive ions immersed in a “sea of mobile (delocalized) electrons. ”24. This substance will not conduct as a solid, but will conduct as a liquid or in solution. 25. OCl226. (diagram)–+–+=­=­+ –-+ –-=­=­27. Which of the following processes requires the least energy?A. Breaking the bond between Na+ and Cl− in NaCl. B. Breaking the bond between H and Cl in HCl. C. Separating two CO molecules. D. Separating two H2O molecules. 28. Which of the following transformations is sublimation?A. Solid GasB. Gas SolidC. Liquid SolidD. Solid Liquid29. Using intermolecular force theory, explain why a substance will change from a gas to a liquid if thetemperature is lowered sufficiently. 30. In terms of electron mobility and electronegativity, explain why Na(s) is a very good conductor of electriccurrent while NaCl(s) is a nonconductor. Unit I—Additional MaterialExercises: Phase Changes (Use after Section I. 35)1. Why is H2O(g) usually called water vapor?2. What is the difference between evaporation and boiling?3. How would it be possible to boil water at room temperature?4. When water is heated to boil, tiny bubbles form on the bottom surface. What gas is inside the bubbles a)initially and b) at full boil?5. a) If we have no frost or built up ice in a freezer and introduce water vapour into the freezer (by opening iton a humid day) what will happen?b) Conversely, I once put a unwrapped snowball in my mother’s freezer in January and by July it was almostshriveled in size to a small pea. What happened?. 6. People will often refer to the boiling point of water as 100C. What is actually meant by this?7. Some non-chemists have argued that the ocean must be less than 10 000 years old based on the followinglogic: a) water carrying salts flows to the ocean from rivers running over mineral rich rocksb) this water and mineral salt solution flows into the seac) only water evaporates from the oceans (the salt is left behind)d) thus the salt concentration of the ocean should increase yearly and the measured salinity of the ocean ismuch less than if the ocean has been here for millions and billions of years. Using LeChatelier’s principle and the reversibility of dissolving and salt crystallization explain how torespond to this charge. 8. Consider the following reversible reaction: N2O4 (g) 2 NO2 (g)If we add in more NO2 we’ll force the reaction further to the _____. Explain using LeChatelier’s Principle. What would happen if added more N2O4?