Chapter 10 States of Matter 10.1 Kinetic Molecular Theory and Gases

POINT > Define the Kinetic Molecular Theory (KMT) POINT > Describe 5 assumptions about an “ideal gas” POINT > Describe properties of gases in terms of KMT POINT > Identify conditions that cause real gases to deviate from “ideal” gas behavior

POINT > Define the Kinetic Molecular Theory (KMT) Literal interpretation: “theory of moving molecules” KMT explains the behavior of gases, liquids, solids and the transitions between these three states Today we will focus on gases

POINT > Identify the FIVE assumptions about an “ideal gas” KMT description of gases is based on five assumptions about an “ideal gas” Ideal gases don’t exist, but most gases do behave this way under most conditions The five assumptions are as follows:

POINT > Identify the FIVE assumptions about an “ideal gas” 1. Gases are composed of tiny particles far apart relative to their size: The volume occupied by the gas molecules is inconsequential; the volume is mostly empty space

POINT > Identify the FIVE assumptions about an “ideal gas” 2. Gas particles are in continuous, rapid, random motion As a result, there are collisions with other molecules or with the wall of the container This creates pressure

POINT > Identify the FIVE assumptions about an “ideal gas” 3. There are no attractive forces between molecules Gas molecules are moving too fast Gas molecules are too far apart Intermolecular forces are too weak

POINT > Identify the FIVE assumptions about an “ideal gas” 4. Collisions between gas particles and between container walls are “elastic” No net loss of total kinetic energy Kinetic energy can be transferred between two particles during collisions Total kinetic energy remains the same as long as temperature remains the same

POINT > Identify the FIVE assumptions about an “ideal gas” 5. All gases at the same temperature have the same average kinetic energy The energy is proportional to the absolute temperature Absolute temperature = Kelvin scale ( ̊ K = ̊ C + 273) Ke = ½ mv2 Ke = kinetic energy m = mass v = velocity

WB CHECK: Which is not an assumption about an ideal gas? a) Gas particles are relatively far apart b) Gas particles exert pressure on the walls of a container due to collisions c) When gas particles collide they lose a small amount of kinetic energy d) Gaseous N2 and H2O at the same temperature will have the same average kinetic energy

WB CHECK: You know from your understanding of polar bonds that water molecules are attracted to each other. Give two reasons why hydrogen bonds don’t form between water vapor molecules

Ke = ½ mv2 tells you that WB CHECK: a) all gas particles move at the same velocity b) all gas particles have the same mass c) collisions between gas particles are elastic d) smaller gas particles have greater velocity

POINT > Describe properties of gases explained by KMT 1. Expansion: Gases fill any container in which they are enclosed, regardless of shape or volume

POINT > Describe properties of gases explained by KMT 1. Expansion: Gases fill any container in which they are enclosed, regardless of shape or volume 2. Fluidity: Gas particles move past each other easily, without interaction, enabling gases to flow

POINT > Describe properties of gases explained by KMT 3. Low density: Particles are relatively far apart (~1000x more so than liquids or solids) 4. Compressibility: Gases are easily compressed relative to liquids or solids, because particles are so far apart

POINT > Describe properties of gases explained by KMT 5. Diffusion: Gases readily diffuse and mix with other gases, due to random motion of both gases 6. Effusion: Gases will move through a tiny opening between vessels until concentrations are equal in both

WB CHECK: Which property of gases is shown below?

WB CHECK: Which two properties of gases are shown below?

POINT > Recognize conditions that cause real gases to deviate from “ideal” gas behavior Most gases act like ideal gases under normal conditions Noble gases and nonpolar gases like N2, H2 behave ideally under the widest range of conditions

POINT > Recognize conditions that cause real gases to deviate from “ideal” gas behavior Polar gases, such as NH3 or H2O, can deviate more than nonpolar gases due to intermolecular interactions Very low temperature or very high pressure will cause gases to deviate from ideal behavior. Why?

WB CHECK: Which gas would be more likely to deviate from ideal gas behavior, Cl2 or HCl? Why?

Homework: Read Pages 311-314 Complete #1-6 Page 314