Ch.5 - GasesSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

A gas is seen as a collection of molecules or individual atoms that are in constant motion. The Kinetic-Molecular Theory tries to use data of real gases to predict how an ideal gas would behave if they existed.  

Examining the Kinetic-Molecular Theory

Concept #1: Understanding the Kinetic-Molecular Theory

Ideal gases are imaginary and don’t actually exist. However, if they did exist then there would be certain characteristics that a gas would need to possess in order to be an ideal gas. 

Concept #2: The Characteristics of an Ideal Gas

Example #1: Two identical 10.0 L flasks each containing equal masses of O2 and N2 gas are heated to the same temperature. Which of the following statements is/are true?  

a) The flask with the oxygen gas will have a greater overall pressure.

b) The nitrogen and oxygen gases will have the same average speed or velocity.

c) The nitrogen and oxygen gases will have the same average kinetic energy.

Additional Problems
Which set of temperature and pressure conditions will cause a gas occupying a volume of 300 mL to deviate from ideal gas behavior? (A) 100°C and 4 atm (B) 100°C and 2 atm (C) —100°C and 4 atm (D) 0°C and 2 atm
The graph (below) shows the distribution of molecular velocities.  How many of the statements are true? At a given temperature, curve A represents gas particles with the smallest molar mass For a given gas sample, curve D represents the highest temperature At a given temperature, curve D represents gas particles with the highest molar mass For a given gas sample, the broader the velocity distribution, the lower the temperature 0                      b) 1                  c) 2                  d) 3                  e) 4 
A change in temperature from 10°C to 20°C is found to double the rate of a particular chemical reaction. How did the change in temperature affect the reacting molecules? (A) The average velocity of the molecules doubled (B) The average energy of the molecules doubled (C) The number of collisions per second doubled (D) The number of molecules above the reaction energy threshold doubled. 
The partial pressure of an ideal gas is equal to:   a) The pressure it would exert if it were at high pressure, same volume, and alone in a container. b) The pressure it woudl exert if it were at low pressure, same volume, and alone in a container.  c) The pressure it would exert if it occupied the same volume, alone in a container, at the same temperature.  d) The pressure it would exert if it were at low temperature, same volume, and alone in a container.  e) The pressure it would exert if it were at high temperature, same volume, and alone in a container.   
Which of these properties is/are characteristic(s) of gases? a) High compressibility b) Relatively large distances between molecules c) Formation of homogeneous mixtures regardless of the nature of gases d) A and B, and C. 
What is different for 100 mL of water at 0°C versus 100 mL of ice at 0°C?   A. Average kinetic energy of molecules. B. The mass. C. Arrangement of atoms within the molecule. D. Size of H2O molecules. 
Which of the following statements is/are true molecules according to the Kinetic Molecular Theory? i. increasing the amount of gas molecules increases the pressure by increasing the force of the collisions. ii. decreasing the temperature of a gas decreases the pressure by increasing the force of the collisions. iii. decreasing the volume of a gas increases pressure by increasing the frequency of the collisions. a. i only b. ii only c. iii only d. i and ii e. ii and iii
If equal masses of O 2(g) and HBr(g) are in separate containers of equal volume and temperature, which one of the following statements is true?   a) The pressure in the O 2 container is greater than that in the HBr container. b) There are more HBr molecules than O 2 molecules. c) The average velocity of the O 2 molecules is less than that of the HBr molecules. d) The average kinetic energy of HBr molecules is greater than that of O 2 molecules. e) The pressures of both gases are the same. 
At the particle level, why do most substances expand when heated? a) The density of the particles increases b) The density of the particles decreases c) The particle motion increases and the spacing between the particles increases d) The particle motion increases and the spacing between particles decreases e) The substances undergo a chemical change
At very high pressures (~ 1000 atm), the measured pressure exerted by real gases is greater than that predicted by the ideal gas equation. This is mainly because a) such high pressures cannot be accurately measured. b) real gases will condense to form liquids at 1000 atm pressure. c) gas phase collisions prevent molecules from colliding with the walls of the container. d) of attractive intermolecular forces between gas molecules. e) the volume occupied by the gas molecules themselves becomes significant.
Which of the following statements is false? a. Condensed states have much higher densities than gases. b. Molecules are very far apart in gases and closer together in liquids and solids. c. Gases completely fill any container they occupy and are easily compressed. d. Vapor refers to a gas formed by evaporation of a liquid or sublimation of a solid. e. Solid water (ice), unlike most substances, is denser than its liquid form (water).
At constant temperature, which of the following statement(s) is/are  TRUE according to the figure?             I)  Every molecule of gas A has a faster speed than every molecule of gas D. II) Gas D has the smallest molar mass. III) Gas B has a smaller molar mass than gas C.   A) I only       B) II only      C) III only        D) both I and III          E) both II and III
Which of the following statements about the phases of matter is TRUE? A) In both solids and liquids, the atoms or molecules pack closely to one another. B) Solids are highly compressible. C) Gaseous substances have long-range repeating order. D) There is only one type of geometric arrangement that the atoms or molecules in any solid can adopt. E) Liquids have a large portion of empty volume between molecules.
According to Kinetic Molecular Theory (KMT), which statement is   TRUE? A. The density of a gas is usually comparable to the density of solids. B. The average kinetic energy of a particle is proportional to the temperature in degree Celsius. C. The collisions of particles with one another are completely elastic. D. A single particle does not move in a straight line. E. At constant temperature, the pressure of a gas in a container will decrease if the volume of the container decreases.
Which is heavier, humid air or dry air?   Briefly explain your reasoning.
Which of the following is one of the postulates of the kinetic theory of gases?   a. The average kinetic energy of the molecules of a gas depends only on the temperature and is independent of the mass of the molecules or the gas density. b. A pure gas consists of a large number of identical molecules separated by distances that are large compared with their size c. Temperature has meaning in a system of gaseous molecules only when their distribution of speeds is the Maxwell-Boltzmann distribution. d. At constant temperature, the volume of a sample of gas is a liner function of its temperature. e. The total pressure of a mixture of gases equals the sum of the portial pressures of the individual gases.
For a substance that remains a gas under the conditions listed, deviation from the Ideal Gas Law would be most pronounced at   1. 0ºC and 2.0 atm. 2. 100ºC and 2.0 atm. 3. -100ºC and 2.0 atm. 4. 100ºC and 4.0 atm. 5. -100ºC and 4.0 atm. 
Which of the following is not part of the kinetic molecular theory?   a. Atoms are neither created nor destroyed by ordinary chemical reactions. b. Attractive and repulsive forces between gas molecules are negligible. c. Gases consist of molecules in continuous, random motion. d. Collisions between gas molecules do not result in the loss of energy. e. The volume occupied by all the gas molecules in a container is negligible compared to the volume of the container
The following information is to be used for the next three problems. A lab bench has three one liter stopped flasks. Flask A contains one mole of NH3 gas. Flask B contains one mole of N2 gas and Flask C contains one mole of SO 2 gas. All are at the same temperature. Which flask has molecules with the greatest average kinetic energy? a. cannot be determined without more information b. all are the same c. A d. B e. C   Which flask has gas with the greatest density in g/L? a. cannot be determined without more information b. all are the same c. A d. B e. C   Which flask has the molecules with the greatest average speed (velocity)? a. cannot be determined without more information b. all are the same c. A d. B e. C
Which of the following statements are false? a. Standard temperature and pressure are 25.0°C and 1.000 atm b. The volume of a fixed quantity of gas maintained at constant temperature is inversely proportional to temperature c. Gas molecules occupy –0.1% of the total volume of a container d. In a given sample of an ideal gas. gas molecule behavior is dependent on molecular attraction and repulsion e. Equal volumes of gases at the same temperature and pressure contain the same numbers of molecules   a) a, c, e b) b, d c) a, b, d d) c, d, e e) b, c, d
An ideal gas differs from a real gas in that the particles of an ideal gas   a. have very large molecular volume b. are assumed to occupy an infinitely small volume c. have a molecular weight of zero d. generally have no kinetic energy e. do not exert any pressure
Which of the following statements is false? a. gases are highly compressible b. distances between molecules of gases are very large compared to bond distances within molecules c. non-reacting gas mixtures are homogeneous d. gases expand spontaneously to fill the container they are placed in e. gases have densities higher than solids
Which of the gases in the graph below has the largest molar mass? A) A B) B C) C D) D E) There is not enough information to determine. ‖
Consider two separate 1 L gas samples, both at the same temperature and pressure. The two gases have different molar masses. Which is true?  1. The particles in both gas samples have different average kinetic energies. 2. You would need more information to be able to compare the average kinetic energies of these two gas samples. 3. The particles in both gas samples have the same average kinetic energies. 
The graph shows the distribution of molecular velocities for the same molecule at two different temperatures (T1 and T2). Which temperature is greater? Explain. 
Which postulate of the kinetic molecular theory breaks down under conditions of high pressure? Explain. 
Which postulate of the kinetic molecular theory breaks down under conditions of low temperature? Explain. 
Which gas molecules have the highest average kinetic energy at a given temperature? a) HBr b) NO2 c) C2H6 d) all have the same
A gas is showing a considerable amount of attractive forces. What is the likely value for the compressibility factor?1. It will be slightly above one.2. It will be slightly below one.3. It will be equal to one.
Which gas has molecules with the greatest average molecular speed at 25°C?A) ArB) N2C) CO2D) CH4 E) Kr
Under what conditions is a gas most likely to deviate from ideal behavior?1. high temperatures2. when considering noble gases3. low density4. high pressure
Deviations from the ideal gas law are less at:a. high temperatures and high pressuresb. high temperatures and low pressuresc. low temperatures and high pressuresd. low temperatures and low pressures
Under which conditions will a gas behave most ideally?1. high T and low P 2. low V and low P3. high P and low V4. high T and low V5. low n and high P6. high T and high n7. high n and high P8. high V and low T9. high n and high V
Which of the following is a postulate of the kinetic molecular theory of gases?a. The volume occupied by the individual particles that compose a gas is very small. However, the distances between gas particles are comparable to the sizes of the gas particles, so the volume occupied by the individual gas particles cannot be assumed to be negligible.b. The particles that compose a gas are so small compared to the distances between them that the volume of the individual particles can be assumed to be negligible.c. Despite being very small, the volume occupied by the individual particles that compose a gas cannot be assumed to be negligible.d. Because the distances between gas particles are so small relative to the sizes of the gas particles themselves, the volume of the individual particles can be assumed to be negligible.
A bottle of highly volatile perfume with molecular formula C5H8O4N2 spills inside a large infinitely expandable bubble and the bubble expands to its maximum size consistent with the fact that the perfume liquid/vapor equilibrium still exists i.e. the perfume “gas” molecules cause the bubble to expand with no work involved. How many molecules of perfume remain in the liquid phase?a. not enough information is given to sayb. 22.4 litersc. none should be left in the liquid phased. one molee. about one or two molecules
The pressure exerted by a gas is caused by a) collisions of the gas molecules with the container. b) the density of the gas molecules. c) the temperature of the gas molecules. d) intermolecular forces. e) the volume that the gas molecules occupy. 
Which of the following statements about gases is true?Heavier gas particles effuse faster than lighter gas particles.Particles of different masses have the same average speed at a given temperature.The higher the temperature, the lower the average kinetic energy of a gas sample.At very high pressures, a gas will occupy a larger volume than predicted by the ideal gas law.Particles of lighter masses have a lower average speed then particles of a higher mass at a given temperature
Select the gas with the highest average kinetic energy per mole at 298 K.a. O2b. CO2c. H2Od. H2e. All have the same average kinetic energy.
Which of the following compounds will behave MOST like an ideal gas at low temperatures? a. H2 b. SO2 c. H2O d. CO2 e. I2
Select the gas with the highest average kinetic energy per mole at 298K:a. O2b. CO2c. H2Od. H2e. All have the same average kinetic energy. 
Which of the following gases has the highest average speed at 400K?A) N2B) O2C) F2D) Cl2
Helium is preferable to hydrogen for filling balloons because helium isa) less dense.b) less expensive.c) easier to obtain.d) chemically inert.
Consider two cylinders of gas. One cylinder contains N2 at 2 atm and 25◦C. The other cylinder contains F2 at 1 atm and 50◦C. Which statements is/are true?I) The N2 molecules and the F2 molecules have the same average kinetic energy.II) Every molecule in the N2 sample has the exact same speed.III) If the pressure of N2 was increased without a change in n or V, the temperature would have to increase.IV) The N2 gas would behave less ideally if the pressure was increased.Which of these statements is true?1. III and IV only 2. I and II only3. II and III only4. II and IV only5. I and IV only
Which of the following statements is/are true? Check all that apply.a) There are gas molecules that move slower than the average speed.b) There are gas molecules that move faster than the average speed.c) All the gas molecules in a sample have the same kinetic energy.d) The average kinetic energy of gas molecules increases with temperature.f) The average speed of gas molecules increases with temperature.
The graph shows the Maxwell distribution plots for a given gas at three different temperatures. Which plot corresponds to the highest temperature?1. B2. Cannot be determined from this type of plot.3. C4. A
The average speed of a gas is dependent only on:a. the temperature of the gasb. the temperature and the mass of the gasc. the temperature, the mass and the density of the gasd. the mass of the gase. the density of the gas
The pressure of a sample of gas describes: A) the speed of the gas moleculesB) the number of gas moleculesC) the number of gas molecules in a set volumeD) the force of gas molecules hitting the surfaceE) the mass of the gas molecules
The graph shows the distribution of molecular velocities. Which of the following statement is TRUE? 
If a real gas has a volume that is larger than you would predict based on the ideal gas law, then the intermolecular forces for that gas are dominated by1. compression forces2. attractive forces3. repulsive forces4. gravitational forces5. neither attractive nor repulsive forces
Which gas sample representation has the greatest pressure? Assume that all the samples are at the same temperature. Explain 
According to the kinetic molecular theory, the pressure of a gas in a container decreases if the     A) number of collisions with the container wall increases.B) temperature of the gas increases.C) another ideal gas is added to the container but volume is kept constant.D) volume of the container increases.
A gas mixture at T = 300.K contains an equal number of moles of chlorine, (Cl  2), ethane (C2H6), nitrous oxide (N2O), and sulfur hexafluoride (SF6). Which gas molecules will have the highest average speed?a. Cl2b. C2H6c. N2Od. SF6e. All of the molecules will have the same average speed
Liquids have a higher vapor pressure at a higher temperature because1. the molar enthalpy of vaporization is decreased as the temperature is raised.2. the more rapidly moving molecules in the gas phase exert a higher pressure on the container walls.3. a higher temperature is required to supply the heat of vaporization of the liquid.4. more molecules in the liquid have enough kinetic energy to escape from the surface.5. the higher temperature may exceed the critical temperature of the liquid.
Consider a 1.0-L sample of helium gas and a 1.0-L sample of argon gas, both at room temperature and atmospheric pressure. b. Do the atoms in the helium sample have the same average velocity as the atoms in the argon sample? 
Consider a 1.0-L sample of helium gas and a 1.0-L sample of argon gas, both at room temperature and atmospheric pressure.  Do the argon atoms, because they are more massive, exert a greater pressure on the walls of the container? Explain. 
A flask at room temperature contains exactly equal amounts (in moles) of nitrogen and xenon.b. The molecules or atoms of which gas have the greater average velocity?
Which of the following gases has the highest average speed at 400K?a. O2b. Cl2c. F2d. Br2e. N2
Which of the following gases has the lowest average speed at 25°C?a. H2Seb. PH3c. C2H6d. F2 
Five samples of helium gas are described in the table below. Rank the samples in order of increasing average kinetic energy of the atoms in them. That is, select "1" next to the sample in which the helium atoms have the lowest average kinetic energy. Select "2" next to the sample in which the helium atoms have the next lowest average kinetic energy, and so on. 
Identify the gas particle that travels the fastest. a. Neb. Cl2c. N2d. COe. H2  
Rank these real gases according to how closely they resemble an ideal gas. CO, N  2, Ne, He, NH3