Upcoming SlideShare
×

Like this presentation? Why not share!

Applied Chapter 12.1 : Characteristics of Gases

on Mar 31, 2010

• 2,354 views

Views

Total Views
2,354
Views on SlideShare
2,334
Embed Views
20

Likes
0
43
0

2 Embeds20

 http://sssd.schoolwires.net 13 http://www.sssd.com 7

Report content

• Comment goes here.
Are you sure you want to

Applied Chapter 12.1 : Characteristics of GasesPresentation Transcript

• Chapter 12.1
Characteristics of Gases
• Describe the general properties of gases.
Define pressure, give the SI unit for pressure, and convert between standard units of pressure.
Relate the kinetic-molecular theory to the properties of an ideal gas.
Objectives:
• Kinetic-Molecular Theory (KMT)
• ·
Based on the idea that particles of matter are always in motion.
Provides a model of an ideal gas
Imaginary gas that perfectly fits all the assumptions of the kinetic-molecular theory.
KMT is based on the following 5 assumptions:
Gases consist of large numbers of particles that are far apart relative to their size.
• Volume of gas particles occupy a volume usually about a thousand times greater than liquid and solid particles.
• Collisions between gas particles and between particles and container walls are elastic collisions.
• Elastic collisions are ones in which there is no net loss of kinetic energy.
Gas particles are in continuous, rapid, random motion. They therefore possess kinetic energy.
• Kinetic energy is the energy of motion.
• There are no forces of attraction or repulsion between gas particles.
• Think of gas particles as small billiard balls, when they collide , they do not stick together, they bounce apart immediately.
The average kinetic energy of gas particles depends on the temperature.
• Higher the temperature, the faster the particles move
• Kinetic-molecular theory and the nature of gases
Expansion:
• Gases do not have definite shape nor volume
• The expand to fill container and take it’s shape and volume
Kinetic-moleculartheory
Gas particles move rapidly in all directions (assumption 3) without significant attraction or repulsion between them ( assumption 4)
• Fluidity
• Ability to flow
• Liquids and gases are considered fluids because they both flow
Kinetic-moleculartheory
Low Density
• Density of a gas is 1/1000ththat of liquid or solids.
Animation
Kinetic-moleculartheory
Particles are so much farther apart in a gaseous state (assumption 1).
• Compressibility
• Crowding particles closer together.
Kinetic-moleculartheory
Gas particles are initially far apart (assumption 1), allowing the particles to be crowded together.
Diffusion
• Spontaneous mixing of the particles of two substances caused by their random motion.
Kinetic-moleculartheory
Random and continuous motion of the molecules (assumption 3) carries them throughout the available space.
• Effusion
• Process by which gas particles pass through a tiny opening.
Animation of Effusion
Source:
http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/gaslaw/micro_effusion.html
• Pressure
To describe a gas fully, there are four measurable quantities
Volume
Temperature
Number of molecules
Pressure
• Pressure and Force
Pressure – defined as the force per unit area on a surface
Pressure =
force
area
Use pressure to explain why it is harder to cut this pineapple with the butter knife.
How do snow shoes work?
How does pressure help us skate?
• force
N
Pressure =
Units:
area
cm2
H0w is a magician able to survive laying on a bed of nails?
• Atmospheric Pressure :
Blanket of air surrounding earth, exerting pressure
• Barometer:
Device used to measure atmospheric pressure.
At OoC, atmosphere can support 760 mm column of mercury.
Units of Pressure:
1 atmosphere or 1 atm
millimeters mercury ormm Hg
torr (in honor of EvangelistaTorricelli)
Pascal, Pa - pressure exerted by a force of one Newton acting on an area of one square meter.
Conversions
1 atm = 760 mm Hg
1 torr = 1 mm Hg
1 atm = 760 torr
1 atm = 1.013 25 x 105 Pa
1 atm = 101.3 25 kPa
• Standard Temperature and Pressure
Scientists have agreed on standard conditions of :
1 atm pressure and O0C
Also known as STP
Sample Problem 1
The average atmospheric pressure in Denver, Colorado, is 0.830 atm. Express this pressure (a) in mm Hg and (b) in kPa.
760 mm Hg
0.830 atm
x
(a)
=
631 mm Hg
1 atm
101.325 kPa
0.830 atm
x
(b)
=
84.1 kPa
1 atm