applied chapter 12.1 : characteristics of gases
TRANSCRIPT
Chapter 12.1
Characteristics of Gases
1. Describe the general properties of gases.2. Define pressure, give the SI unit for
pressure, and convert between standard units of pressure.
3. 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:
1. Gases consist of large numbers of particles that are far apart relative to their size.o Volume of gas particles occupy a volume
usually about a thousand times greater than liquid and solid particles.
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2. Collisions between gas particles and between particles and container walls are elastic collisions.o Elastic collisions are ones in which there is
no net loss of kinetic energy.
3. Gas particles are in continuous, rapid, random motion. They therefore possess kinetic energy.o Kinetic energy is the energy of motion.
4. There are no forces of attraction or repulsion between gas particles.o Think of gas particles as small billiard balls,
when they collide , they do not stick together, they bounce apart immediately.
5. 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
1. Expansion: Gases do not have definite shape nor volume The expand to fill container and take it’s
shape and volume
Kinetic-molecular
theoryGas particles move rapidly in all directions (assumption 3) without significant attraction or repulsion between them ( assumption 4)
2. Fluidity Ability to flow Liquids and gases are considered fluids
because they both flow
Kinetic-molecular
theory
3. Low Density Density of a gas is 1/1000th that of liquid or solids.
Kinetic-molecular
theoryParticles are so much farther apart in a gaseous state (assumption 1).
Animation
4. Compressibility Crowding particles closer together.
Kinetic-molecular
theoryGas particles are initially far apart (assumption 1), allowing the particles to be crowded together.
5. Diffusion Spontaneous mixing of the particles of two substances
caused by their random motion.
Kinetic-molecular
theoryRandom and continuous motion of the molecules (assumption 3) carries them throughout the available space.
6. Effusion Process by which gas particles pass through a tiny
opening.
Animation of Effusion
http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/gaslaw/micro_effusion.html
Source:
PressureTo describe a gas fully, there are four
measurable quantitiesVolumeTemperatureNumber of moleculesPressure
Pressure and ForcePressure – defined as the force per unit
area on a surfacePressure = force
area
Use pressure to explain why it is harder to cut this pineapple with the butter knife.
How does pressure help us skate?
How do snow shoes work?
Pressure = force
area
N
cm2Units:
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
1 atm = 760 mm Hg
millimeters mercury or mm Hgtorr (in honor of EvangelistaTorricelli)Pascal, Pa - pressure exerted by a force of one Newton acting on an area of one square meter.
Conversions1 torr = 1 mm Hg1 atm = 760
torr1 atm = 1.013 25 x 105 Pa1 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 1The average atmospheric pressure in Denver, Colorado, is 0.830 atm. Express this pressure (a) in mm Hg and (b) in kPa.
0.830 atm
=760 mm Hg1 atm
x 631 mm Hg
(a)
0.830 atm
=101.325 kPa1 atm
x 84.1 kPa(b)