Honors Chemistry
Think about it: Kinetic Molecular Theory
Team members Names ______________________________________
Learning Objectives
1. Identify the basic differences between particle behavior in the solid, liquid, and
gaseous phases.
2. Develop an understanding of the postulates of the kinetic molecular theory.
3. Identify how temperature affects molecular motion.
4. Apply the kinetic molecular theory to predict the outcome of everyday situations.
Model 1: Representation of Atoms in Different Phases
The following figures show the representative particles of a given substance in various
states of matter.
Note: Give complete answers to the key questions, exercises, and problems. Provide
explanations and show work, where necessary.
Key Questions
1. What are the key characteristics of atoms and molecules in gases, liquids, and
solids? In Table 1 below, describe the characteristics of particles for each phase of
matter based on Model 1. Be specific with regard to spacing, the potential of particles
movement, and whether or not the particles will fill the container.
Table 1: Characteristics of the Phases of Matter
Solid
Liquid
Spacing
Relative Density
Movement
Relative Kinetic
Energy
Volume (Shape)
Modified from Foundations of Chemistry by David Hanson Page 2 of 3
Gas
2. _________________________ In which phase of matter is there the least spacing
between particles?
3. _________________________ In which phase of matter is there the most potential
for movement?
4. _________________________ Which phase of matter does not have a definite
shape yet the particles will not fill the container?
5. In terms of arrangement and motion, what is necessary to change from a solid to a
liquid?
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6. What is this process called? ____________________________________________
7. How is this process accomplished? (Think Energy)
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8. In terms of arrangement and motion, what is necessary to change from a solid
directly to a gas?
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9. What is this process called? ______________________________
10. How is this process accomplished?
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Model 2: Postulates of the Kinetic Molecular Theory
 Gases consist of tiny particles (atoms or molecules).
 These particles are so small compared with the distance between them that the
volume(size) of the individual particles can be assumed to be negligible (zero).
 The particles are in constant random motion, colliding with the walls of the
container. These collisions with the walls cause the pressure exerted by the gas.
 The particles are assumed to not attract or repel each other.
 The average kinetic energy of the gas particles is directly proportional to the
Kelvin(absolute) temperature of the gas.
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Key Questions:
11. What causes a gas to exert pressure when confined in a container?
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12. How does the total volume of gas particles compare to the volume of the space
between gas particles?
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13. As the temperature of a gas decreases, what change occurs in the amount of kinetic
energy?
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14. What property of gas particles is measured by temperature?
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15. What is the relationship between temperature and molecular motion?
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16. In terms of the kinetic molecular theory of gases, explain how increasing the
temperature of a gas confined in a rigid container causes an increase in the pressure
of the gas?
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Applications
17. There is a government warning on all aerosol cans that states:
Do not store at a temperature above 120ºF (50ºC).
a. Explain why this warning is required in terms of the relationship between
temperature and pressure and the kinetic molecular theory.
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b. What could happen if an aerosol can was heated above 120°F (50°C)?
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18. How does the kinetic molecular theory explain why 1 mol of krypton and 1 mol of
helium have the same volume at STP?
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19. The graph on the right shows the
distribution of molecular velocities of a gas
at two different temperatures.
a.) Does curve 1 or 2 better represent the
behavior of the gas at the lower
temperature? Explain your reasoning.
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b.) Which curve represents the sample with the higher average kinetic energy,
Ek (average)? Explain your reasoning.
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c.) Which curve represents the sample that diffuses more quickly? Explain your
reasoning.
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d.) Suppose that curves 1 and 2 represent two different gases at the same
temperature. If the gases are helium and neon, match the curves with each gas.
Explain your reasoning.
Hints:
i.) Substances at the same temperature have the same average kinetic energy;
ii.) Kinetic Energy of a particle is related to the mass of the particle and its
velocity: Ek = ½mv2
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