The Kinetic-Molecular Theory of Matter Objective 2.05

Ideal Gases ► An imaginary gas that perfectly fits all the assumptions about kinetic molecular theory ► Kinetic Molecular Theory of Gases (KMT)  explains the properties of gases

Kinetic-Molecular Theory of Gases ► Assumptions about Ideal Gases  particles are spread far apart  mostly empty space  Collisions are elastic collisions  Particles are in continuous, random motion  no forces of attraction or repulsion  average kinetic-energy = temperature

However……. ► Real Gases  Do not follow KMT completely  But we can use the KMT to describe them  How they differ: ► Occupy space ► Particles ARE attracted to each other (to some degree) ► Nonpolar gases deviate less than polar gases

Nature of gases explained by KMT ► Expansion ► Fluidity ► Low Density ► Compressibility ► Diffusion

Units of pressure ► Mm of Hg ► Torr ► Atmospheres (atm) ► Kilopascals (kPa) ► Pressure Unit Conversions  1 atm = 760 mmHg = 760 torr = kPa

Units of Temperature ► Celsius (˚C) ► Kelvin (K) K = ˚C + 273

Standard temperature and pressure (STP) ►1►1►1►1 atm…OR 777760 mm Hg 777760 torr 111101.3 kPa ►2►2►2►273 K (0° C)

The Gas Laws ► Combined Gas Law P 1 V 1 = P 2 V 2 T 1 T 2 T 1 T 2 Used to determine pressure, temperature or volume of a gas

Examples of Gas Problems using Combined Gas Law ► Pg. 315 Sample Problem 10-2 ► Pg. 318 Sample Problem 10-3 ► Pg. 320 Sample Problem 10-4 ► Pg. 321 Sample Problem 10-5 ► Remember T must be in Kelvin! ► Remember P units must be all the same! ► Whichever unit is constant cancels out!!!

The Gas Laws ► Boyles Law: ► Charles Law: ► Gay Lussac’s Law

Ideal Gas Law ► Mathematical relationship among pressure, volume, temperature, and the number of moles of a gas ► PV=nRT (given on Reference Guide)  Pressure (P)  Volume (V)  Number of moles (n)  Ideal gas constant (get from table on sheets)  Temperature (T)

Examples of Ideal Gas Problems ► Pg. 342 Sample Problem 11-3 ► Pg. 343 Sample Problem 11-4 ► Pg. 344 Sample Problems 11-5

Dalton’s Law of Partial Pressures ► The total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases ► P T =P 1 +P 2 +P 3 +… (given on reference guide) ► Also…for gas collected over water  P T = P gas + P H2O

Example of Partial Pressures Problem ► Pg. 324 Sample Problem 10-6 ► To get water pressure use ► Water Vapor Pressure Table Appendix A pg 899

Avogadro’s Law for Gases ► Gases of the same volume, at the same temp and pressure, have the same number of molecules! ► n/V = n/V ► A mole ratio in an equation can become a VOLUME ratio when all compounds are gases

Example of Avogadro’s Law H 2 (g) + Cl 2 (g)  2HCl (g) Mole Ratio: 1 mol:1mol:2mol Volume Ratio: 1L : 1L :2L

Molar Volume of A Gas ► At STP 1 mole of any gas = 22.4 L New Branch on Mole Map