Syllabes of 331 chem course• Kinetic theory.• Forces between atoms, ions and molecules.• Colligative properties. Vapor pressure and enthalpy. Boiling

and freezing. • Solid phase and its structure. Solubility and dissociation• Phase equilibrium. • Ideal and non-ideal solutions . Solvent and solute activities.

Ion hydration. • Born and Debye-Hükle models. • Activity coefficient. Electrolytic conductance. Ionic mobility.

Transport number. Diffusion, transport and Fix’s laws.• Formation of colloidal dispersions, Colloid stability, Reference of course Physical chemistry, Gordon Barow, Ch 1,2,9,10,17

331 chem courseReference of these Slides :1. James Brady2. (Meteorology Today) Prof. Jin-Yi Yu3. (from The Blue Planet) ESS55 Prof. Jin-Yi Yu4. (Harcourt school Publishers) 5. Lecture Plus Timberlake 2000

Objective for gases • Revision of Characteristics of Gases, ideal gas law,

Dalton’s law of partial pressures.• Kinetic Molecular Theory :• Kinetic energy of gases, molecular speed• Deviations from ideal behaviour• Condensation of gases

GASES (Harcourt school Publishers)

A windy day or a still day is a result of the difference in pressure of gases in two different locations.

What are the important Characteristics of Gases ??

Gases have a number of Properties such as: 1) Gases are compressible2) Gases exert pressure3) Gas pressure depends on the amount of

confined gas4) Gases fill their container5) Gases mix freely with each other (infinitely

miscible)6) Gas pressure increases with temperature

7)Gases have low viscosity (Gases flow much easier than liquids or solids)

Boyle’s Law

• Hyperbolic Relation Between Pressure and Volume

p

V

p – V Diagramp – V Diagram

isotherms

T1 T2 T3 T3 >T2>T1

(courtesy F. Remer)

Charles’ Law

• Linear Relation Between Temperature and Pressure

P

T (K)0 100 200 300

P – T DiagramP – T Diagram

isochorsisochorsV1 V2

V3

V1 <V2 <V3

(courtesy F. Remer)

What is the ideal gas law ??

K.mol .atm L 0.0821

constant gas universal

RnRTPV

How can we calculate Gas density & Molecular mass?? PV= nRT = m RT M PM =m RT = d RT VPM= dRT

(from Meteorology Today) Prof. Jin-Yi Yu

Question 1:Explain the following graph.The atmospheric pressuredecreases exponentially With height .

Question 2:If a helium balloon 1 m in diameter is released at sealevel will it expand or shrink why?

(from The Blue Planet) ESS55Prof. Jin-Yi YuExampleIf a helium balloon 1 m in diameter is released at sealevel, it expands as it floatsupward because of thepressure decrease. Theballoon would be 6.7 m indiameter as a height of 40km.

What is Mole fraction? ?: For a mixture of A, B, … substances, mole

fraction of substance i (Xi)

What is Dalton’s law of partial pressures ??

innnn

nX iZBA

AA of moles ,

...

...1....

....

BA

TotalBTotalA

BATotal

XXPXPX

PPPiP

from James BradeyGases are often collected over water , they are saturated

with water vapor. The pressure this vapor exerts is called the vapor pressure

As gas bubbles through water, water vapor gets into the gas so the total pressure inside the bottle includes the partial pressure of the water vapor.

• The total pressure is the pressure of the gas plus the vapor pressure of water vapor

760.0 100 55.32 40 31.82 30 17.54 20 4.579 0

(torr) PressureVapor C)( eTemperatur o

Vapor pressure of water at various temperatures.

aporwatertotalgas

aporwatergastotal

PPP

PPP

v

v or

Ideal Gas Model  Kinetic Molecular Theory (KMT) for an ideal gas

states that all gas particles:1. Gas consists of large number of particles (atoms or

molecules) hard spheres of insignificant volume 2. are in random, constant, straight-line motion. 3. are separated by great distances relative to their size.4. have no attractive forces between them. 5. have collisions that may result in the transfer of

energy between gas particles, but the total energy of the system remains constant. Newtonian Mechanics is used.

What is the Kinetic Energy &Avg speed of a molecule ??Compare KEavg of two different gases at the same temp.

KE (one mole) = 3/2 RTKE (one molecule ) = 3 RT = 3 kB T 2NA 2 R= gas constant, NA = Avogadro's Number , kB is Boltzmann’s constant

KE (one molecule) = (1/2)mµ2 KE (one mole) = NA (1/2)mµ2 = (1/2)Mµ2

Avg velocity of one mole gas µ2 = 3RT M

m is the mass of a gas particle , M is the molecular mass.

Maxwell distribution :In 1859, James Clerk Maxwell (1831 – 1879) worked out a formula for

the most probable distribution of speeds in a gas . Molecules in a gas sample move at a variety of speeds . speed of each molecule constantly changing due to countless collisions(about 1 billion per second for each molecule).At low temperature most molecules move close to the average speed , at higher temperature there is greater distribution of speeds.

Maxwell distribution of speeds :

Just for your knowledge do not memorize

Brownian motion. Chaotic motion of minute particle suspended in a gas or liquid

GASES (Harcourt school Publishers)

Ideal vs. Non-Ideal Gases

• Kinetic Theory Assumptions– Point Mass– No Forces Between Molecules– Molecules Exert Pressure Via Elastic Collisions

With Walls

xx

(courtesy F. Remer)

Ideal vs. Non-Ideal Gases

• Non-Ideal Gas– Violates Assumptions

• Volume of molecules• Attractive forces of molecules

(courtesy F. Remer)

Deviations from ideal behaviour Question :At what condition a real gas behaves like an ideal

gas ??• A real gas behaves like an ideal gas when the real

gas is at low pressure and high temperature. • At high pressures gas particles are close therefore

the volume of the gas particles is considered.• At low temperatures gas particles have low

kinetic energy therefore particles have some attractive force

• Example• Dry ice, liquid oxygen and nitrogen

State Differences between ideal gases & real gases

• Real gases behave as described by the ideal gas equation; no real gas is actually ideal.

• Within a few %, ideal gas equation describes most real gases at room temperature and pressures of 1 atm or less.

• In real gases, particles attract each other reducing the pressure.

• Real gases behave more like ideal gases as pressure approaches zero.

What is wrong in this graph???

James BradeyDeviation from ideal gas law. A plot of PV/T versus P for an ideal gas is a straight line. The same plot for oxygen is not a straight line.

Results for Real Gases

(a) In an ideal gas, molecules would travel in straight lines. (b) In a real gas, the paths would curve due to the attractions between molecules.

Deviations from ideal behavior occur because:1) Gas molecules interact and2) Gas molecules occupy a finite volume

J. D. van der Waals corrected the ideal gas equation into :

The constants a and b are called the van der Waals constants a, b are different for each gas

valuegas ideal to measured reduces :

valuegas ideal toup measured increases : 2

2

2

2

Vnb

PV

an

nRTnbVV

anP

measured

measuredmeasured

measured

• At sea level the atmospheric pressure is about 14.7 psi

• Other common pressure units are the bar:1.00 atm =760mmHg =14.7 psi =1.0133 bar

0.03049 5.464 OH Water,0.03707 4.170 NH Ammonia,0.02661 0.02444 H Hydrogen,0.01709 0.2107 Ne Neon,0.02370 0.03421 He Helium,

mol L

mol atmL Substance

2

3

2

122

ba

Temperature Scale