Gas Properties and Behavior

Chapters 13 and 14 Prin.of Chem

Properties of Gases - KMT

1. Mostly empty space 2. Particles are always moving (fast) 3. Volume depends on temp and pressure 4. Shape depends on the container (earth??) 5. Kinetic energy of particles determines speed. (temp)

Gas Pressure



Pressure

: the force acting on a unit area of a surface (example: force per square centimeter) 

Atmospheric pressure

: 14.7psi (pounds per square inch) at sea level; 1 atm 

Kinetic Theory

: all matter is composed of particles in constant motion.



Gas pressure

is caused by the gas particles hitting the sides of the container.

Pressure

Defined: Force per unit area Occurs when particles collide with walls of container.

-more collisions = more pressure

Kinetic Energy, Speed, and Temp.

 KE is energy of motion  Temperature is a measure of average KE  Both are linked to the speed of the particles TEMP.

KINETIC ENERGY (SPEED)

Atmospheric pressure

Air pressure or barometric pressure (comes from the weight of the air)

Barometric pressure

Higher at sea level than on top of mountains.

Why????

Ideal gases

A gas that is described by the kinetic molecular theory (model)

Kinetic Model - Gases

Group of statements that describe physical characteristics of gases.

1. made of very tiny atoms 2. move constantly, straight lines, random 3. very far apart (particle volume is almost zero) 4. collisions cause pressure and conserve energy.

Pressure

Measured with a barometer or pressure gauge.

Units are: mmHg (common) or psi (USA only) Pascal (official SI unit) but is really tiny or kilopascal (more likely) or Atmosphere (my favorite)

1 atm Pressure

Barometer



At one atmosphere

pressure a column

of mercury 760 mm high.

Column of Mercury

Dish of Mercury

11

Pressure Conversions



Standard (Equivalent) Pressure

: at sea level  1.0 atm = 760 mmHg = 14.7 psi = 101.3 kPa  Problem: Tire pressure gauge reads 35psi. What is the equivalent in kilopascals?

 (35psi) x 101.3 kPa = 240 kPa 14.7 psi

Make conversions

Change 2.0 atm to kPa 2.0 atm x 101.3 kPa = 202.6 kPa 1.0 atm

Temperature

  

Fahrenheit

– common, not scientific

Celcius

– used everywhere, except USA, based on water MP = 0 °C BP = 100°C  Absolute zero = -273 °C

Kelvin

– (Absolute temperature) used for all gas law calculations • absolute zero 0 °K = no motion of atoms • No negative temp

.

•

K = C + 273

Kelvin Temperature Scale



Absolute Zero

= zero kinetic energy; particles are not moving at all. Absolute zero has never been reached.



Kelvin Scale

: directly proportional to kinetic energy of particles.

  Celsius 100 o C   0 o C -273 o C Kelvin 373 273 0

STP

 Standard Temperature and Pressure – Used to compare measured gases in diff. experiments.

 1 atm pressure and 273 K  At STP 1.0 mole of any gas occupies 22.4 L

The Gas Laws

 Statements which predict gas behaviors  Math relationships  Mostly common sense.

Laws cont.

 Daltons law of partial pressure.

– In a mixture of gases, the total pressure equals the sum of all the individual gases.

Boyles law

• Pressure and volume are inversely proportional (when the temp. stays the same) • P 1 x V 1 = P 2 x V 2 • If the pressure doubles the volume is cut in half.

Boyle’s Law Cont.



Graph

resembles a curve.

 

Kinetic theory explanation

: compressing the air (making the volume smaller) creates less space for the particles to travel = more hits = greater pressure. Expand the volume & the particles must travel farther to hit the sides of the container = less hits = lower pressure.

Charles Law

• Volume and Temperature are directly proportional (pressure is constant) • • V 1 T 1 = V 2 T 2 • If the temperature doubles, the volume doubles

Charles’s Law cont.

 

Graph

is a straight line  

Kinetic Theory Explanation

greater volume. : When the gas particles are heated, they speed up (increase kinetic energy) = more hits on the sides of the expandable container (balloon) = When the gas particle are cooled, they slow down= fewer hits = less volume

Gay Lussac Law

• Pressure and Temperature are directly proportional (volume is constant) • • P 1 T 1 = P 2 T 2 • If the Temperature doubles, the pressure doubles

Temperature & Gas Pressure

 High temperature makes particles speed up = more hits on the sides of the container = greater pressure.

 Cold temperature makes particles slow down = fewer hits = lower pressure

Combined Gas Law

• Boyles, Charles, and Gay Lussac Laws all together…..

• P 1 V 1 T 1 = P 2 V 2 T 2 • Keep track of the units - temp. must be in Kelvins, P and V must be same on both sides.

The Ideal Gas Law

• • • Relationship between pressure, temp. volume and number of moles (particles).

Can be used to find info about any gas.

PV = nRT • • • P is pressure(atm or kPa) V is volume (L) n is number of moles(mol) T is temperature (K) and R is the ideal gas constant