Warm-Up
Label your new warm-up/cool-down log
“The Properties of Gases”
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?
Chapter 13.1 The Nature of
Gases
Chapter 13.1 The Nature of
Gases
After this section 13.1, we will move onto
Chapter 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 Hg
1 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 atm
o
0C
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?