Transcript Chapter 13 States of Matter

Chapter 13
States of Matter
13.1 The Nature of Gases
• Kinetic refers to
motion…kinetic energy
• The kinetic theory states
that tiny particles in all
forms of matter are in
constant motion
Three basic assumptions of the kinetic
theory as it applies to gases:
#1 Gas is composed of
particles…molecules or atoms
- small, hard spheres
-insignificant volume, far apart from
each other
-no attraction or repulsion between
particles
#2 Particles in a gas move rapidly
in constant random motion
-move in straight paths,
changing direction only when
colliding with each other or other
objects
-average speed of O2 in air at
20° C is 1700km/h
#3 Collisions are perfectly
elastic
-total kinetic energy remains
constant
• Gas Pressure – the force
exerted by a gas per unit
surface area of an object
• Due to:
1) Force of collisions
2) Number of collisions
What if there are no
particles?
•No collisions
•No pressure
•Vacuum
Atmospheric Pressure
• Results from the collisions of
air molecules with objects
• What happens if you climb to
the top of a mountain…or dive
deep in the ocean?
Measuring Pressure
• Evangelista Torricelli created the
first barometer
• Baro = weight
• Meter = measure
Barometer
• Measures
atmospheric
pressure
• Depends on
weather and
altitude
SI unit of pressure, pascal, Pa
• At sea level, atmospheric
pressure is about 101.3 kPa,
kilopascals
• Older units of pressure
–Millimeters of mercury
(mm Hg)
–Atmospheres (atm)
Using a mercury barometer…
• at sea level, the Hg
would rise to a
height of 760 mm at
25° C
• This is called one
standard
atmosphere (atm)
• For gases it is important to relate
measured values to standards:
–Temperature of 0° C
–Pressure of 101.3 kPa, or 1 atm
Standard Temperature & Pressure
STP
What happens when a
substance is heated?
• Some of the energy is stored in
the particles…called?
• It does not raise the temperature
• Remaining energy speeds up the
particles, increases average
kinetic energy  increasing
temperature also
• The particles in any
collection have a wide
range of kinetic energies,
but most are somewhere in
the middle...
• So we use the term
average kinetic energy
• An increase in the average kinetic
energy of particles causes the
temperature to rise
• As it cools, particles move more
slowly and average K.E. decreases
• Will they ever slow down enough
to stop moving?
• The particles
would have no
kinetic energy
because no
motion
–Absolute zero
(0 K or -273° C)
• The Kelvin temperature of
a substance is directly
proportional to the average
kinetic energy of the
particles of the substance