Warm-Up

At 20oC, molecules in the air move over 1000 mph. At this speed, the smell of pizza made in LA should reach our school in about 30 minutes.

Why don’t we smell all of these fast moving molecules?

Label your new warm-up/cool-down log“The Properties of Gases”

Chapter 13.1 The Nature of Gases

Chapter 13.1 The Nature of Gases

After this section 13.1, we will move ontoChapter 14, “The Behavior of Gases”

Today’s Learning Objectives

--What KMT theory is and its five main assumptions--Know difference between ideal and real gases--Know how scientists define pressure--Be able to convert between various pressure units--How a barometer works--What STP is

Kinetic Molecular Theory (KMT) of Gases

• KMT is a model to explain the behavior of gaseous particles

• A gas is ideal (ideal gas) if we make the following 5 assumptions of KMT

KMT Assumptions

• Particles are in constant, random, straight line motion. They possess energy in motion, kinetic energy.

• The actual volume of gas particles is negligible. Particles are far apart.

KMT Assumptions

• Particles are in constant, random, straight line motion. They possess energy in motion, kinetic energy.

• The actual volume of gas particles is negligible. Particles are far apart.

KMT Assumptions

• Gas particles do not attract or repel.

• The average kinetic energy of a collection of gas particles is directly proportional to the Kelvin temperature of the gas.

KMT Assumptions

• Gas particles do not attract or repel.

• The average kinetic energy of a collection of gas particles is directly proportional to the Kelvin temperature of the gas.

KMT Assumptions

• Collisions between gas particles and between particles and container are “elastic” collisions

• An elastic collision means no loss of kinetic energy (KE)

KMT Assumptions

• Collisions between gas particles and between particles and container are “elastic” collisions

• An elastic collision means no loss of kinetic energy (KE)

Real Gas vs Ideal Gas

KMT breaks down at low temperatures and very high pressures

KMT breaks down the more polar the gas is ---- Helium gas is more ideal than water vapor

Pressure

Pressure is defined as the force per unit area on a surface …..

Pressure = force/area (N/cm2 or N/m2)

Earth’s atmosphere pushes down on us with pressure of 10.1 N/cm2 (1.03 Kg per cm2)

Measuring Pressure - Barometer

Units of Pressure

1 mm Hg – millimeters of Mercury 1 torr = 1 mm Hg1 atm = 760 mm Hg = 760 torr(average atmospheric pressure at 0oC at sea level)

SI Unit is the Pascal (Pa) – Pressure of one Newton acting on 1 m2

1 atm = 101.325 kPa = 101,325 Pa

Standard Temperature and Pressure

1 atm0oC

Called STP

Homework

-Read Chapter 13.1-Page 407 #26-34

Cool Down?

If you read a pressure gauge at 670 kPa, how many atmospheres of pressure is there?