The Kinetic Molecular Theory States of Matter—Gases, Liquids and Solids

The Kinetic Molecular Theory Literal interpretation: The theory of moving molecules

The Kinetic Molecular Theory Observations to support the theory: Diffusion in gases and liquids Movement of substances from an area of high concentration to one of lower concentration Ability of a gas to spread out and fill a container Brownian Movement The observable movement of particles due to collisions with moving molecules.

The Kinetic Molecular Theory The theory explains these observations The theory describes the differences between gas, liquids and solids The theory explains the gas laws

The Kinetic Molecular Theory Major points: Supports the concept of an ideal gas… An ideal gas is one that perfectly fits all the assumptions of the kinetic-molecular theory. Do not actually exist—in theory this is how they would behave:

The Kinetic Molecular Theory 1. Gases are made of tiny particles far apart relative to their size: Volume occupied by the molecules is inconsequential Volume is mostly space Explains why gases are compressible

The Kinetic Molecular Theory 2. Gas particles are in continuous, rapid, random motion As a result there are collisions with other molecules or with the wall of the container Creates pressure Increase in temperature increases the movement of the molecules and thus the pressure exerted by the gas

The Kinetic Molecular Theory 3. There are no attractive forces between molecules under normal conditions of temperature and pressure Gas molecules are moving too fast Gas molecules are too far apart Intermolecular forces are too weak

The Kinetic Molecular Theory 4. Collisions between gas particles and between particles and container walls are elastic collisions. Collisions in which there is no net loss of total kinetic energy Kinetic energy can be transferred between two particles during collisions Total kinetic energy remains the same as long as temperature remains the same

The Kinetic Molecular Theory 5. All gases at the same temperature have the same average kinetic energy. The energy is proportional to the absolute temperature. Absolute temperature = Kelvin temp scale Ke = ½ mv2 Ke = the kinetic energy m = mass v = the velocity

The Kinetic Molecular Theory 1. Gases are made of tiny particles far apart relative to their size 2. Gas particles are in continuous, rapid, random motion 3. There are no attractive forces between molecules under normal conditions of temperature and pressure 4. Collisions between gas particles and between particles and container walls are elastic collisions. 5. All gases at the same temperature have the same average kinetic energy. The energy is proportional to the absolute temperature.

The Kinetic Molecular Theory Applies only to ideal gases Most gases behave like an ideal gas under normal conditions Gases with little attraction between molecules…He/H2/N2 Real gases Deviate from ideal behavior Due to intermolecular interaction (H2O, NH3) High pressure Low temperature

The Kinetic Theory and Changes of State Gases—Attractions are insignificant Liquids—Attractions are more important leading to a more ordered state Solids –Attractions are most important with an ordered state

Kinetic Molecular Theory and Changes of State Attractions between particles in strength: Least London dispersion forces Dipole-dipole interaction Hydrogen bonding Greatest Metallic, Ionic and Covalent network

Kinetic Molecular Theory and Changes of State Changes of state occur with a change in temperature or pressure Particles of a substance overcome (or succumb) to intermolecular attraction Involves energy

Kinetic Molecular Theory and Changes of State Solids, liquids and gases can undergo various changes in processes that are either endothermic or exothermic

Kinetic Molecular Theory and Changes of State Consider the evaporation of a liquid: Temperature= the average kinetic energy Some molecules have more kinetic energy than others These molecules escape and become gas molecules

Kinetic Molecular Theory and Changes of State Evaporation will occur in closed container also except…… As the liquid evaporates the space above starts to fill with gas molecules until it can hold no more Gas will start to condense.

Kinetic Molecular Theory and Changes of State Eventually the rate of evaporation will equal the rate of condensation Two processes will occur simultaneously with no net change State of Equilibrium Vapor molecules above the liquid will collide with each other and the container………………………and exert a pressure. Equilibrium vapor pressure!!!

Kinetic Molecular Theory and Changes of State Every liquid has a specific vapor pressure at a given temperature. Reflection of the strength of the intermolecular bonding between molecules Vapor pressure also increases with temperature

Kinetic Molecular Theory and Changes of State Equilibrium vapor pressure is (EVP) used to define boiling point, BPt Boiling point is the temperature at which the equilibrium vapor pressure equals atmospheric pressure

Kinetic Molecular Theory and Changes of State Boiling point of water is 100 oC only at 760mm Hg When atmospheric pressure is > 760 mm Hg the boiling pt is > 100. When atom0spheric pressure is <760mm Hg the boiling pt is <100

Kinetic Molecular Theory and Changes of State Boiling requires a continuous supply of energy…….. Water boils at 100oC and the temperature does not change….even though there is a continuous supply of energy….. Where does the energy go?

Kinetic Molecular Theory and Changes of State Same is true when ice melts…… It melts (or freezes) at 00C At this temperature there is a state of equilibrium Temp will not change if both phases are present

Kinetic Molecular Theory and Changes of State Energy is can be added continuously, but the temperature does not change Energy is used to change the physical state…this requires a lot of energy!!

Kinetic Molecular Theory and Changes of State The amount of heat energy required to melt one mole of a solid at the solid’s melting point is the solid’s molar enthalpy of fusion. DHf Energy absorbed represents potential energy For water it is 6.009kJ/mol Xj/g =6.009kJ/M x 1M/18g x 1000J/1kJ = 333.8 j/g

Kinetic Molecular Theory and Changes of State The amount of heat energy required to vaporize one mole of a liquid at the liquid’s boiling point is the liquid’s molar enthalpy of vaporization. DHv Energy absorbed represents potential energy For water it is 40.79kJ/mol Xj/g =40.79J/M x 1M/18g x 1000J/1kJ = 2266 j/g

Kinetic Molecular Theory and Changes of State Compared to other substances these values are very high. Water has very strong intermolecular bonding Hydrogen bonds between highly polar molecules

Kinetic Molecular Theory and Changes of State Unique properties of water is related to the hydrogen bond 4-8 molecular groups in liquid water Hexagonal arrangement in solid --> Dipole w/ partial +/-  High boiling pt of water  Solid is less dense..Ice floats

Changes of State are Shown in Phase Diagrams Changes of phase are depicted in phase diagrams Show the relationship between state of matter, temperature and pressure

Changes of State Shown in Phase Diagrams Phase diagrams define: Triple point=the T/P conditions at which all three phases coexist Critical point = Critical temp and press Critical temp = temp above which the substance cannot exist as a liquid Critical press= lowest pressure at which the substance can exist as a liquid at the critical temperature

Phase Diagram of Water Interesting points AD—Ice and vapor in equilibrium AC– Liquid and vapor in equilibrium AB—Ice and liquid in equilibrium. Note an increase in pressure lowers melting point nbp=normal boiling pt mp =melting point Critial temp =373.99

Phase Diagram of Carbon Dioxide Note the following: Very different temp and pressure compared to water’s diagram Liquid is only possible at high pressure At normal room conditions CO2 only exists as a gas

Phase Change vs Temperature change in a single phase Melting/Fusion …Molar heat of fusion 6.009 kJ/mol Vaporizing Molar hear of vaporization 40.79kJ/mol Raising the temperature of a homogeneous material Specific heat

Phase Change How much energy is absorbed when 47g of ice melts? (at STP) Energy =47g x 1 mol x 6.009kJ 18g 1 mol = 15.7 kJ

Phase Change How much energy is absorbed when 47g of water vaporizes? (at STP) Energy =47g x 1 mol x 40.79kJ 18g 1 mol = 106 kJ (vs 15.7 kJ—gases have a higher energy content)

Phase Change What mass of steam is required to release 4.97 x 105kJ of energy when it condenses? grams =4.97 x 105kJ x 1mol x 18g 40.79kJ 1 mol = 2.19 x 105 g

Temperature change in a single phase Specific heat of water , Cp Definition… the quantity of heat (q) required to raise 1 gram of water 1oC at a constant pressure. Value will vary for each substance

Temperature change in a single phase Quantity of energy transferred as heat while a temperature change occurs depends on The nature of the substance The mass of the material The size of the temperature change. Water has a high specific heat Metals have low specific heat Units = J/(g x oC)

Temperature change in a single phase Specific heat of water (l) = 4.18 J/goC Specific heat of water (s) = 2.06 Specific heat of water (g) = 1.87 Specific heat of ethanol (g) = 1.42 Specific heat of ethanol (l) = 2.44 Specific heat of mercury (l) = 0.140 Specific heat of copper (s) = 0.385 Specific heat of lead (s) = 0.129 Specific heat of aluminum (s) = 0.897

Solids and the Kinetic Molecular theory Properties: Dominated by the fact that Closely packed particles Relatively fixed positions Highest intermolecular or interatomic attractions Properties are Definite shape and volume Definite melting point High density and incompressibility Low rate of diffusion

Solid structure Solids may be crystalline Solids may be amorphous Crystals in which particles are arranged in a regular repeating pattern Particles are randomly arranged

Solid structure Crystals Total 3-D arrangement of particles is the crystal structure CUBIC BODY CENTERED CUBIC TETRGONAL HEXAGONAL TRIGONAL MONO

4-Classes of Crytsalline Solids Ionic --Ions Hard and Britle Covalent Network Network of molecules Quartz (SiO) Diamond Metallic Crystals Free moving e- Covalent Molecular Crystals Weak…. Water, dry ice

Amorphous solids Without shape No regular pattern Glasses Plastics