States of Matter Chapter 2 Dr. Mohammed Suleiman
Binding Forces between Molecules TheThree States of Matter: In order for molecules to exist in aggregates in gases, liquids and solidsIntermolecular forces must exist
Repulsive and Attractive Forces As two atoms or molecules are brought closer together, the opposite charges and binding forces in the two molecules are closer together than the similar charges and forces, causing the molecules to attract one another. The negatively charged electron clouds of molecules largely govern the balance (equilibrium) forces between the two molecules When the molecules are brought so close that the outer charge clouds touch, they repel each other like rigid elastic bodies
Repulsive and Attractive Forces Repulsion and the intermolecular 3D structure 1,2-Dimethylcyclopentans Has two conformation cis trans The trans conformation is energetically favored due to the a minimization of the repulsive force
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) “Measure” of intermolecular force boiling point melting point DHvap DHfus DHsub Generally, intermolecular forces are much weaker than intramolecular forces.
Intermolecular Forces Adhesion Cohesion Cohesion is the intermolecular attraction between like molecules Adhesion is an attraction between unlike molecules Hg H2O
Types of attractive Intermolecular Forces Types of inter. Forces: • Keesom forces (Dipole-dipole) Van der Waal forces • Dipole-induced dipole • Dispersion (London forces) • Ion-dipole • Hydrogen bonding Depending on the phase of a substance, the nature of Chemical bonds, and the type of element present, more than one type of inter. can be present between the molecules
Permanente dipole Peptide bond ᵟ- ᵟ+ ᵟ- ᵟ+
Orientation of Polar Molecules in a Solid Intermolecular Forces Dipole-Dipole Forces Attractive forces between polar molecules Max. attractive interaction In liquid polar molecules are not held as rigidly as in solid
Ion-Dipole Interaction Intermolecular Forces Ion-Dipole Forces Attractive forces between an ion and a polar molecule
Interaction Between Water and Cations in solution Hydration is one example of ion-dipole interaction
Intermolecular Forces Dispersion Forces Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules He atom or Non-polar molecule ion-induced dipole interaction He atom or Non-polar Molecule dipole-induced dipole interaction
Induced Dipoles Interacting With Each Other Instantaneous dipole it lasts for tiny fraction of second This type of interaction is responsible for the condensation of non-polar gases as He and N2
Dispersion Forces Benzene Orbital overlap
Intermolecular Forces Dispersion Forces depends on: 1. Charge on the ion and the strength of the dipole 2. 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 • (i.e. large atom) Dispersion forces usually increase with molar mass.
O O S 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. CH4 CH4 is nonpolar: dispersion forces. SO2 SO2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO2 molecules.
What type(s) of intermolecular forces exist between the following of the following pairs: (a) HBr and H2S (b) Cl2 and CBr4 (c ) I2 and NO3- (d) NH3 and C6H6 ? (a) HBr and H2S Both are polar H---Br Therefore, the intermolecular forces present are: Dipole –dipole forces ,as well as dispersion forces
(b) Cl2 and CBr4 Both are nonpolar Only dispersion forces between these molecules c) I2 and NO3- I2 is homonuclear diatomic molecule and therefore nonploar NO3- anion The forces between both are Ion-induced dipole and dispersion forces
(d) NH3 and C6H6 NH3 is polar C6H6 is nonpolar The forces: dipole-induced dipole forces and dispersion forces
or … … H H B A A A Intermolecular Forces Hydrogen Bond The hydrogen bond is a special dipole-dipole interaction between they hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. A & B are N, O, or F
Intermolecular Forces Hydrogen Bond The average strength of a hydrogen bond is quite large ~ 40kj/mol Hydrogen bond have powerful effect on the structure and Properties of many compounds The strength of a hydrogen bond is determined by the coulomb Interaction between the lone-pair of the electronegative atom and the hydrogen nucleus. Fluorine is more electronegative than oxygen HF(l) have stronger hydrogen bond than H2O(l)
Which of the following can form hydrogen bonds with water? CH3OCH3, CH4, F- , HCOOH, Na+ No electronegative elements (F, O or N ) in either CH4 an Na+ CH4 can not form hydrogen bond Na+can not form hydrogen bond CH3OCH3, F-, and HCOOH can form hydrogen bond
Which of the following species are capable of hydrogen bonding among themselves? (a) H2S (b) C6H6 (c) CH3OH CH3OH only
3-D Structure of ice Ice is less dense than water Intermolecular Forces Hydrogen Bond Water Unusual properties of water: • High dielectric constant • Abnormal low vapor pressure • High boiling point
Hydrogen Bond Salicylic acid andIter.&Itra.Hydrogen bonding ASPIRIN Hydrogenfluoride HF
The Bond Energy It’s a measure of the strength of the bonds H bond is relatively weak(2 to 8 kcal/mole) are much weaker than the covalent bond (100kcal/mole) and ionic bond (> 100kcal/mole) Energies associated with molecular and ionic interaction
The Three States of Matter Phase : homogenous part of a system with well defined boundary 2 phases Energy (heat) Solids with higher vapor pressure, as iodine and camphor, can pass directly to the gaseous phase without melting (sublimation) Certain asymmetricmoleculesfrequently exhibit fourth phase, termed (mesophase), which lies between the liqiud and crystalline states called liquid crystalline state
Freeze Drying (Lyophilization) is a dehydration process typically used to preserve a perishable material or make the material more convenient for transport. Freeze-drying works by freezing the material and then reducing the surrounding pressure and adding enough heat to allow the frozen water in the material to sublime directly from the solid phase to the gas phase. 0.006 atm
Freeze Drying (Lyophilization) Freeze drying is used is industry and pharmacy for the manufacturing heat-sensitive drug Freeze dried Cafe Water soluble medicines
The Three States of Matter Force Area Gaseous state Gases are in constant random motion Pressure = (force = mass x acceleration) Units of Pressure 1 pascal (Pa) = 1 N/m2 1 atm = 760 mmHg = 760 torr 1 atm = 101325 Pa
The Three States of Matter Boyle’s law: P a (at constant n and T) Va nT nT nT P P P V = constant x = R 1 V Gaseous state Ideal Gas Equation Charles’ law: VaT(at constant n and P) Avogadro’s law: V a n(at constant P and T) R is the gas constant PV = nRT
R = (1 atm)(22.414L) PV = nT (1 mol)(273.15 K) The conditions 0 0C and 1 atm are called standard temperature and pressure (STP). Experiments show that at STP, 1 mole of an ideal gas occupies 22.414 L. PV = nRT R = 0.082057 L • atm / (mol • K)
The Three States of Matter Gaseous state The molar gas constant R PV = nRT R = PV/nT = 1atm (L) / Mol(K) At STP condition ( 0 °C and 1atm) it was found experimentally that 1 mol of any gas occupy 22.414 L R = 0.082 L . atm /mol . K 1J= Kg m2/s2= 1Nm 1 dyn = 1 g·cm/s² = 10−5 kg·m/s² = 10 µN R = 8.314 J/mol K 1 joule = 107 erg and 1 cal = 4.184 J R = 1.987 cal/mol deg
In the assay of ethyl nitrite spirit, the nitric oxide gas that is liberated from a definite quantity of spirit and collected in a gas burret occupies a volume of 30 mL at a temperature of 20°C and a pressure of 740 mmHg. Assuming that the gas is ideal, what is the volume at 0°C and 760 mmHg ? Synthesis of ethyl nitrite Used for cold & Flu However FDA has blocked over-the-counter sales of this same remedy, known in the USA as sweet nitrite or sweet spirit of nitre since 1980
1 mol HCl V = n = 49.8 g x = 1.37 mol 36.45 g HCl 1.37 mol x 0.0821 x 273.15 K V = 1 atm nRT L•atm P mol•K What is the volume (in liters) occupied by 49.8 g of HCl at STP? T = 0 0C = 273.15 K P = 1 atm PV = nRT V = 30.7 L
d = m V M = PM = RT dRT P Density (d) Calculations m is the mass of the gas in g M is the molar mass of the gas Molar Mass (M ) of a Gaseous Substance d is the density of the gas in g/L
If 0.3 g of ethyl alcohol in the vapor state occupies 200 mL at a pressure of 1atm and a temperature of 100°C, what is the molecular weight of ethyl alcohol? Assume that the vapor presser behaves as and ideal gas
KE = 3/2RT KE = ½ mu2 Kinetic Molecular Theory of Gases • A gas is composed of molecules that are separated from each other by distances far greater than their own dimensions. The molecules can be considered to be points; that is, they possess mass but have negligible volume. • Gas molecules are in constant motion in random directions, and they frequently collide with one another. Collisions among molecules are perfectly elastic. • Gas molecules exert neither attractive nor repulsive forces on one another. • The average kinetic energy of the molecules is proportional to the temperature of the gas in kelvins. Any two gases at the same temperature will have the same average kinetic energy
Kinetic Molecular Theory of Gases For the last postulates, the following fundamental kinetic equation is derived Where P is the pressure and V the volume occupied by any number n of molecules of mass m and velocity We can obtain the root mean square velocity usually written as Because nm/V is equal to density (d), we can write
What is the root mean square velocity of oxygen (molecular weight 32) at 25°C (298K) ?
The van der Waals Equation for Real Gases n = = 1.0 PV RT Deviations from Ideal Behavior 1 mole of ideal gas Repulsive Forces PV = nRT Attractive Forces
The van der Waals Equation for Real Gases Effect of intermolecular forces on the pressure exerted by a gas.
} } corrected pressure corrected volume an2 V2 The van der Waals Equation for Real Gases Van der Waals equation nonideal gas ( ) P + (V – nb) = nRT
A 0.193 mole of sample of ether was confined in a 7.35 L essel at 295 K. Calculate the pressure produced using (a) the ideal gas equation (b) the van der Waal equation. (the van der Waal value of a for ether is 17.38 L2atm/mol2 the b value is 0.1344 L/mol
Calculate the pressure of 0.5 mol CO2 gas in a fire extinguisher of 1 liter capacity at 27 °C using the ideal gas eqn. and the van der Waal eqn. (the van der Waal constants ( a & b) can be calculated from the critical Temperature Tc and the critical pressure Pc)
The Three States of Matter The Liquid state Effect of Temperature on Kinetic Energy Methods of achieving Liquefaction 1. Use freezing mixture Subject a gas into intensive cold using a freezing mixture 2. Diabetic expansion The gas is expands so rapidly that no heat enters the system T2 > T1 The work done to bring expansion comes on the expense of the gas heat energy as a result the gas T falls Repeating the process many times cause the gas to liquefies 3. Joule-Thomson effect Highly compressed nonideal gas expands into a region of low p The T decrease results from the energy expended in overcoming the attraction force b/w molecules 4. High p in closed camber at T < Tc
The Three States of Matter The Liquid state The critical temperature (Tc) is the temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure. The critical pressure (Pc) is the minimum pressure that must be applied to bring about liquefaction at the critical temperature.
Aerosols Gases can be liquefied under high pressure in a closed container as log as its kept below Tc. The drug is dissolved or suspended in a propellant; a material which is L under the p condition of the container and its gas under atmospheric conditions e.g. of propellant CFC’s and HFC’s Ethyl chloride is used as antiseptic when sprayed into skin it freezes the tissue so that it can be used as local anesthesia
H2O (l) H2O (g) Dynamic Equilibrium Rate of evaporation Rate of condensation = The equilibrium vapor pressure is the vapor pressure measured when a dynamic equilibrium exists between condensation and evaporation