CHEMISTRY 20 LESSON PLAN Unit Topic: Forms of Matter: Gases
General Learner Outcome 1
· Explain molecular behaviour, using models of the gaseous state of matter
Lesson Topic:
· Properties of gases
Objectives:
· (B1.1k) Describe and compare the behaviour of real and ideal gases in terms of kinetic molecular theory.
· (B1.2sts) Explain that the goal of science is knowledge about the natural world
o Describe examples of natural phenomena and processes and products (such as breathing, diffusion, weather, hot air balloons, scuba diving equipment, automobile air bags, gas turbines and internal combustion engines) that illustrate the properties of gases.
Text References:
· Nelson Chemistry p. 146-149;163
· Inquiry into Chemistry p. 96-101
· Living By Chemistry p. 275-276 Audio/Visual Aids:
Special Facilities:
Lesson Description
· Discussion of general properties of gases and the Kinetic Molecular Theory.
Preparation for Next Class
Chemistry 20 – Kinetic Molecular Theory (KMT)
· Gases are quite different from liquids and solids. The molecules and atoms in solids and liquids are held close together by attractive forces between molecules and atoms.
o Remember: London Force, dipole-dipole force and hydrogen bonding.
· Liquids lie in the bottom of any container they are in, and solids generally maintain their own shape without a container. In contrast, the molecules in gases expand to fill whatever space they are in. this indicates that there are essentially no forces between the molecules in a gas.
· Macroscopic properties of gases are properties that can be directly observed using your senses or a measuring device:
o Gases are compressible.
o Gases expand as the temperature is increased if the pressure remains constant.
o Gases have very low resistance to flow – a property called viscosity.
o Gases have much lower densities that solids or liquids.
o Gases mix evenly and completely when put in the same container. Substance that mix completely with each other are said to be miscible.
· So why is it that gas molecules are found throughout their container and that the space a gas occupies expands so dramatically with temperature?
· Properties of gases are explained by a model called the Kinetic Molecular Theory (KMT).
· This model proposes that gas particles of an ideal gas – atoms or molecules – are in constant motion.
· An ideal gas is defined by the following characteristics:
o The gas particles are in constant, random motion.
o The gas particles travel in straight lines until they collide with other gas particles or with the container walls.
o The particles of an ideal gas are point masses – that is, the have mass but occupy no space (the particles of gas are so small compared to the volume of the container they are in that this is essentially true).
BIG IDEA: On a particle level, all matter is in constant motion.
· Although no gas is ever ideal, the theory quite accurately describes the behaviour of real gases (such as CO
2and O
2) at ordinary temperatures and pressures.
· Since gases have mass, heavier gases (larger molar masses) will move slower than lighter gases at the same temperature (Temperature is actually a measure of the average kinetic energy – speed – of the particles in a substance).
· The illustrations below show the motion of three gas particles at three different times based on the kinetic molecular theory:
Lesson Summary
How is gas behaviour explained?
The kinetic molecular theory (KMT) describes the motions of gas particles – atoms or molecules. The particles in a gas are constantly moving with an average speed that increases with increasing
temperature.
Key Terms
Macroscopic
Viscosity
Miscible
Ideal gas
Point mass
Elastic collision
Chemistry 20 – Kinetic Molecular Theory Problems 1. Identify which macroscopic property
explains the following real-life situations:
a. A full propane tank can provide enough fuel for an entire season of bar-be-ques.
b. The label on a can of hairspray contains the warning “caution may explode when heated.”
c. A carbon monoxide leak in the basement spreads quickly thoughout the house.
d. Forced air heating is often a better choice for home heating than hot water.
e. A bicycle tire develops a small hole and very rapidly becomes flat. Use one of the characteristics of gases to explain why the tire deflates so quickly.
2. Explain the meaning of point mass.
3. How does an elastic collision differ from an inelastic collision? To picture an inelastic collision, imagine throwing a ball of putty against a wall.
4. Why is it important that the molecules of an ideal gas have only elastic collsions?
5. The following figure shows three possible paths for a gas molecule moving inside a filled volleyball. Which of these diagrams represents the most likely path of the gas molecule? Justify your choice in terms of the kinetic molecular theory.
6. Use the kinetic molecular theory to explain:
a. The miscibility of gases.
b. Why gases expand to fill the size of their container.
c. Why gases can be easily
compressed.
Chemistry 20 – Kinetic Molecular Theory Problems - Answers
3.
(a)
Gases are compressible. Since gases are compressible, they cannot be sold by volume, but are instead sold by mass. Most tanks used on domestic barbeques will hold 9 kg of propane.
(b)
Gases expand as the temperature is increased if the pressure remains constant. When a can of hairspray is heated, the volume of the gas will be become too large to be contained by the can and the can will explode.
(c)
Gases have a very low resistance to flow and mix evenly and completely. Many toxic gases are also colourless and odorless, which makes them even more dangerous to transport.
(d)
Gases mix evenly and completely and have a low resistance to flow, which makes it much easier to move the hot gas through a building. Large buildings cannot be heated with forced air, however, because air’s low specific heat capacity compared to water does not permit the storage of sufficient energy to heat a large area.
(e)
Gases have low viscosity. When a hole in a bicycle tire appears, it takes very little time for the air to squeeze out through the hole. (One way to measure viscosity is to see how quickly a fluid (i.e., a liquid or gas) can get through a small opening.)
4.
The space between gas particles is huge compared to the size of the particles themselves. We can simplify the kinetic molecular theory by assuming that the particles have negligable size but do still have a mass.
5.
No kinetic energy is lost by the particles in an elastic collision. In an inelastic collision, some or all of the kinetic energy is lost by the particles in the form of heat.
6.
The definition of an ideal gas assumes that the total kinetic energy of a gas sample is conserved when the particles collide with one another and with the container. In other words, the collisions are elastic. Collisions in real gases are inelastic; therefore some kinetic energy is converted to thermal energy and may be transferred from the system to the surroundings.
8.
Figure (a), since it shows a random pattern to its motion, with straight lines of travel between collision with the container wall and other particles.
9.
(a)
The molecules of a second gas are able to fit into the spaces between the molecules of the first gas.
(b)
The molecules are in constant random motion, so if the container is expanded the molecules will travel further before contacting the walls of the container.
(c)