States of Matter
Phase Change DIagram
Phase Change
Temperature remains during a phase change. Water phase changes
Phase Diagram
What is a phase diagram? (phase diagram for water) Normal melting point: melting point at one atmosphere triple point: T and P at which all three states coexist in equilibrium critical point: beyond this point the vapor cannot be liquified at any pressure Normal boiling Point: boiling point at one atmosphere
Boiling Point and Freezing Point Review the phase diagram of a pure substance. How will the phase diagram of a solution (freezing and boiling points) differ from those of a pure solvent?
Phase Diagram Water Everything else
Water
Carbon dioxide Phase Diagram for Carbon dioxide
Carbon Phase Diagram for Carbon
Kinetic Theory A couple of assumptions! Ideal Gas molecules: Are small, hard spheres with insignificant volume Have no attractive or repulsive forces Move in a fast, constant, random-straight line motion Have perfectly elastic (kinetic energy is transferred without loss) collisions This represents an ideal gas
Properties of Gases Pressure (P) atm (atmospheres) kpa (kilopascals) Volume (V) Temperature (T) Liters K Kelvin Moles (n) Number of moles
Units of Pressure, Temperature, and Volume Units of Pressure: 1 kilopascal (kpa) = 1000 pascals (Pa) 1 torr = 1 millimeter of mercury (mm Hg) 1 atmosphere = 760 mm Hg 1 atmosphere = 101.3 kpa 1 atmosphere = 14.7 lb/in 2 Units of Volume: 1 liter (L) = 1 cubic decimeter (dm 3 ) 1 milliliter (ml) = 1 cubic centimeter (cm 3 ) Temperature Conversions: F = (9/5) C + 32 C = (5/9)( F 32) K (Kelvins) = C + 273 C = K -273
Gas Pressure Gas pressure- the pressure exerted by a gas on an object. This pressure is exerted along the total surface area of the object. Pressure=Force/Area Units of Pressure and Conversions 1 atm=101.3 kpa=760 Torr= 760 mm Hg
Some other important definitions Boiling Point- the temperature of a substance that is reached when the vapor pressure of that substance is greater than or equal to the atmospheric pressure. Atmospheric Pressure-the pressure exerted by the gas molecules in the atmosphere upon any object. Vapor pressure the pressure exerted by a gas above a liquid in a sealed container
Effect of Pressure on Boiling Point
An Early Barometer The normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high.
Physical Characteristics of Gases Gases assume the volume and shape of their containers. Gases are the most compressible state of matter. Gases will mix evenly and completely when confined to the same container. Gases have much lower densities than liquids and solids.
Compressibility Compressibility is a measure of how much the volume of matter decreases under pressure Gasses expand to fill their container Gasses are easily compressed
Compressibility At RT, the distance between particles is about 10x the diameter of the particle This empty space makes gases good insulators (example: windows, fluffy coats) Q: How does the volume of the particles in a gas compare to the overall volume of the gas?
The Gas Laws Boyle s Law P 1 V 1 = P 2 V 2 assuming constant temperature and number of moles. Charles Law V 1 /T 1 = V 2 /T 2 assuming constant pressure and number of moles.(t must be in K). Gay Lussac s Law P 1 /T 1 = P 2 /T 2 assuming constant volume and number of moles.(t must be in K.)
Pressure and Volume A plot of V versus P results in a curve. Pressure and volume are inversely proportional when pressure increases, volume decreases, and vice versa
Volume vs. Temperature Volume and Temperature are directly related when temperature increases, volume increases, and vice versa
Pressure vs. Temperature Pressure and Temperature are directly related when temperature increases, pressure increases
More Gas Laws The Combined Gas Law P 1 V 1 /T 1 = P 2 V 2 /T 2 assuming constant number of moles. The Ideal Gas Law PV = nrt where n=number of moles and R is the gas constant R = 8.31 kpa L/mol K R = 0.0821atm L/mol K.
Molar mass From Periodic Table KNOWN Ratio from Balanced Equation UNKNOWN Molar mass From Periodic Table Grams A Moles A Moles B Grams B 22.4 L/mol IF at STP OR PV = nrt if NOT STP 22.4 L/mol IF at STP OR PV = nrt if NOT STP Volume A if a GAS Volume B if a GAS
Deviations from Ideal Gas Behavior When does one encounter problems when using the ideal gas law? At extremely high pressures. Low temperatures Why? Because our assumptions aren t true! Gas molecules have volume Gas molecules do have attraction to each other
Gas Laws In the air there are a variety of different gases. Dalton s Law The partial pressures of the component gases add together to create the total pressure of the mixture. P 1 + P 2 +..P n = P T In a sealed vessel of dry, nitrogen has a partial pressure of 79.11 kpa, oxygen has the partial pressure of 21.22 kpa, carbon dioxide has a partial pressure of 0.04 kpa and argon and others have a partial pressure of 0.95. What is the total pressure of dry air?
#6 Dalton s Law. And wet gasses? Dalton s Law is particularly useful in calculating the pressure of gases collected over water. Collecting a gas over water many gas-collecting experiments involve this.
Phase Changes Courtesy www.lab-initio.com
A phase is a homogeneous part of the system in contact with other parts of the system but separated from them by a welldefined boundary. 2 Phases Solid phase - ice Liquid phase - water 11.1
Intermolecular Forces Intermolecular forces are attractive forces between molecules. Intramolecular forces hold atoms together in a molecule. Intermolecular vs Intramolecular 41 kj to vaporize 1 mole of water (inter) 930 kj to break all O-H bonds in 1 mole of water (intra) Generally, intermolecular forces are much weaker than intramolecular forces. Measure of intermolecular force boiling point melting point DH vap DH fus DH sub 11.2
1. Hydrogen Bond (strongest) Types of Intermolecular Forces The hydrogen bond is a special dipole-dipole interaction between the hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. IT IS NOT A BOND. A H B or A H A A & B are N, O, or F 11.2
11.2 Hydrogen Bond
Why is the hydrogen bond considered a special dipole-dipole interaction? Decreasing molar mass Decreasing boiling point 11.2
Types of Intermolecular Forces 2. Ion-Dipole Forces Attractive forces between an ion and a polar molecule Ion-Dipole Interaction 11.2
11.2
Types of Intermolecular Forces 3. Dipole-Dipole Forces Attractive forces between polar molecules Orientation of Polar Molecules in a Solid 11.2
Types of Intermolecular Forces 4. Dispersion Forces van der Walls forces/london forces (weakest) Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules ion-induced dipole interaction dipole-induced dipole interaction 11.2
4. Dispersion Forces Continued Intermolecular Forces Polarizability is the ease with which the electron distribution in the atom or molecule can be distorted. Polarizability increases with: greater number of electrons more diffuse electron cloud Dispersion forces usually increase with molar mass. 11.2
What type(s) of intermolecular forces exist between each of the following molecules? HBr HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules. CH 4 CH 4 is nonpolar: dispersion forces. S SO 2 SO 2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO 2 molecules. 11.2
Intermolecular Forces
Intermolecular forces are attractive forces between molecules. (Example: water molecule to water molecule) Intramolecular forces hold atoms together within in a molecule. (Example: H to O bond within a water molecule). Intermolecular vs Intramolecular 41 kj to vaporize 1 mole of water (inter) 930 kj to break all O-H bonds in 1 mole of water (intra) Generally, intermolecular forces are much weaker than intramolecular forces. Measure of intermolecular force boiling point melting point DH vap DH fus DH sub 11.2
Intermolecular Forces 1. London Forces (a.k.a. Dispersion Forces) Weakest 2. Dipole-Dipole Interactions 3. Ion-Dipole Interactions -(Salt dissolving in solution; Na+ and Cl- ) 4. Hydrogen Bonding (STRONGEST)
London Dispersion Forces: Weakest Occur between every compound and arise from the net attractive forces amount molecules which is produced from induced charge imbalances Figure 10-8 Olmsted Williams The larger the molecule the greater it s Dispersion Forces are. Animation: http://chemmovies.unl.edu/chemanime/lo NDOND/LONDOND.html Figure 10-9 Olmsted Williams
The boiling point of long molecules increase with the length of the carbon chain. Olmsted Williams Fig 10-10 Pg 437
How molecular shape affects the strength of the dispersion forces The shapes of the molecules also matter. Long thin molecules can develop bigger temporary dipoles due to electron movement than short fat ones containing the same numbers of electrons. Butane has a higher boiling point because the dispersion forces are greater. http://www.chemguide.co.uk/atoms/bonding/vdw.html
Polarizability the ease with which the electron distribution in the atom or molecule can be distorted. Polarizability increases with: greater number of electrons more diffuse electron cloud Dispersion forces usually increase with molar mass. 11.2
Is the Molecule Polar? The more Electronegative atom will pull the electron density of the bond Closer to itself giving it a partial negative charge leaving the other Atom with a partially positive charge. This is a dipole moment.
Molecules with 3 Atoms CO 2 Even though the C-O bond is polar, the bonds cancel each other out because the molecule is linear the dipole moments are equal and in opposite directions.therefore CO 2 is non-polar. HCN The dipole moment between H-C points in the direction of C. The dipole moment points between C-N points in the direction of the N. Therefore the dipole vectors are additive and HCN is polar SO 2 SO 2 is a polar molecule because the S-O dipole Moments don t cancel each other out due to the angle
Molecules with 4 Atoms CCl 4 is non-polar CHCl 3 is polar
How to Determine if a Molecule Is Polar 1. Draw Lewis Structure 2. If all of the regions of electron density are bound to the same thing (CCl 4 ; CO 2 ) than the molecule is non-polar 3. If the regions of electron density are not bound to the same thing (atom) than the molecule is polar (HCN; SO 2 )
Which of the following molecules are polar (have a dipole moment)?h 2 O, CO 2, SO 2, and CH 4 O dipole moment polar molecule S dipole moment polar molecule H O C O H C H no dipole moment nonpolar molecule H no dipole moment nonpolar molecule 10.2
Dipole-Dipole Forces Attractive forces between polar molecules Orientation of Polar Molecules in a Solid Animation: http://chemmovies.unl.edu/chemanime/dipoled/dipoled.html 11.2
Dipole Forces occur between molecules containing a dipole moment. The positive end of the dipole moment on one mole is attracted to the Negative end of the dipole moment on a nearby molecule. 2-methyl propane (left) and acetone (right) Both compounds are about Equal in size and shape Figure 10-11 Olmsted Williams
Ion-Dipole Forces Attractive forces between an ion and a polar molecule Ion-Dipole Interaction The larger the charge the stronger the force 11.2
Olmsted Williams Fig 10-34 A molecular picture showing the ion-dipole Interaction that helps a solid ionic crystal dissolve in water. The arrows indicate ion-dipole interactions.
What type(s) of intermolecular forces exist between each of the following molecules? HBr HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules. CH 4 CH 4 is nonpolar: dispersion forces. S SO 2 SO 2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO 2 molecules. 11.2
The Hydrogen Bond STRONGEST INTERMOLECULAR http://chemmovies.unl.edu/chemanime/hybond/hybondd.html FORCE Animation
water has water water the has has water the has water highest has the heat highest the lowest the heat highest of of molar fusion melting mass vaporization point boiling point The melting point, boiling point, heat of fusion and heat of vaporization of water are extremely high and do not fit the trend of properties relative to molar mass within Group VIA.
Water exhibits these unusual properties because of hydrogen bonding between water molecules.
A hydrogen bond is an intermolecular bond. A hydrogen bond is formed between polar molecules that contain hydrogen covalently bonded to a small, highly electronegative atom: F, O, N. F H O H N H
it will be attracted to another F, O, or N, on another molecule. A dipole-dipole bond bond will be formed between the two molecules which is called a hydrogen bond. hydrogen bond covalent bond covalent bond
13.8 Water in the liquid and solid states exists as groups in which the water molecules are linked together by hydrogen bonds.