The Kinetic-Molecular The Kinetic-Molecular Theory of Matter Theory of Matter

(KMT)(KMT)

What is the kinetic molecular What is the kinetic molecular theory?theory?

• Theory developed by scientists to explain the behavior of atoms that make up matter

• KMT is used to describe interactions between molecules in solids, liquids, and gasesgases

5 Assumptions of KMT for Gases5 Assumptions of KMT for Gases

NOTE: KMT only applies to idealideal gases gases.1)Gases are made of tinytiny particles that are

far apart far apart from each other (almost like the particles have no volumeno volume).

2)Collisions between gas particles or between gas particles and the walls of their container are elastic collisions (no elastic collisions (no loss of kinetic energy).loss of kinetic energy).

3) Gas particles are in constant, rapid, and random motion because they have kinetickinetic (motion) (motion) energy.

5 Assumptions Cont’d5 Assumptions Cont’d

4) There are no intermolecular forces no intermolecular forces (IMFs) between gas particles.

5) TemperatureTemperature affects the amount of motion the gas particles have (which makes perfect sense since temperature is a measure of the amount of kinetic energy in a sample).

POP QUIZ: POP QUIZ: What are the four types of intermolecular forces?

Properties of Gases & KMTProperties of Gases & KMT

• ExpansionExpansion: Gases do not have a definite shape or a definite volume and they will completely fill any container.

• FluidityFluidity: Gas particles glide easily past one another, like liquids.

• Low DensityLow Density: The density of gases is about 1/1000 the density of solids and liquids.

• POP QUIZ: POP QUIZ: Which assumptions of KMT explain these?

More PropertiesMore Properties

• Compressibility: Compressibility: The volume of gases can be greatly decreased without liquefying.

• Diffusion and Effusion: Diffusion and Effusion: Gases spread out and mix with each other, even without being stirred.

• POP QUIZ 1: POP QUIZ 1: What is the difference between diffusion and effusion?

• POP QUIZ 2: POP QUIZ 2: Which assumptions of KMT explain these properties?

Real GasesReal Gases• A real gas real gas is a gas that does not completely

follow the five assumptions of KMT.• Real gases have volumevolume and have IMFsIMFs.– Low pressure Low pressure and high temperatures high temperatures make real

gases almost like ideal gases– The less polar less polar a gas molecule is, the more like

an ideal gas it is (EX – noble gases and diatomic elements)

• POP QUIZ 1POP QUIZ 1: Explain why low pressures and high temperatures would be good.

• POP QUIZ 2POP QUIZ 2: Explain why less polarity would be good.

• POP QUIZ 3POP QUIZ 3: How do you tell if a gas is polar or nonpolar