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CHEM ON-RAMPS: UNIT 3 (STATES OF MATTER)
PART 2 EXAM REVIEW EXAM QUESTIONS AND
ANSWERS 2024
Kinetic molecular theory
- Gases are all hard spheres
- They are small relative to size of system volume
- They undergo elastic collisions and don't stick or reactā¢ They have a T equal system T that gives all of them the sameEk
- They all have the same Ek, butEk=Ā½ mv2so they have different velocity as inverse square of mass m1v1^2= m2v2^2 also applies to diffusion and effusion m1d1^2= m2d2^ ā¢Velocities in vacuum >> than velocities when diffusing through gases When two samples of ideal gases have the same ?, their molecules must have the same ?. 1.Temperature; speed 2.Volume; mass 3.Density; mass 4.Density; average kinetic energy 5.Mass; average kinetic energy 6.Pressure; average kinetic energy 7.Temperature; average kinetic energy
- Temperature; average kinetic energy Which of the following statements are both true and explained by the kinetic molecular theory of gas? I)Gas molecules typically have velocities of hundreds of meters per second at room temperature. II)There is an inverse square root relationship between temperature and gas velocity. III)The smaller the molecular weight of a gas, the faster it diffuses. IV)Intermolecular attractions between gas molecules reduce the effective pressure of the system. a)I and III only
b)I, II, III, and IV c)I, II, and III only d)I only a)I and III only Which of the following molecules of the following gases will have the greatest average kinetic energy? a) CO2 at 0.1 atm and 298 K b) H2 at 0.5 atm and 298 K c) N2 at 1 atm and 298 K d) All of the molecules have the same kinetic energy d) All of the molecules have the same kinetic energy Ideal Gas Conditions ā¢P is low so don't collide ā¢V is large so don't collide ā¢n is small so don't collide ā¢T is large so don't stickā¢ Also gases are small and nonpolar so don't stick Van der Waals equation to correct non-ideality(P + a correction factor) (V + b correction factor) = nRT What do a and b correct for? a - corrects for stickiness (intermolecular attraction). Large gases and polar gases have large a. small nonpolar gases have small a b --corrects for size. Large molecules have large b. small molecules have small b Gas X has a larger value than gas Y for the Van der Waals constant "a". This indicates that 1.The molecules of X have stronger intermolecular attractions for each other than the molecules of Y have for each other 2.The molecules of X are larger than the molecules of Y 3.The molecules of gas X have a higher velocity than the molecules of gas Y 4.The molecules of has X repel other X molecules 1.The molecules of X have stronger intermolecular attractions for each other than the molecules of Y have for each other correct You cannot always use kinetic molecular theory and the Ideal gas law to explain the behavior of gases. Under which conditions would this theory not be able to explain gas behavior? a)low pressures, low temperatures, and low volumes b)low pressures, high temperatures, and high volumes
- kj/mole 5, Dipole-Dipole, dominant in polar molecules
- kj/mole 20, H bond (Remember Hydrogen Bonding is "F.O.N", and always draw lewis structure before selecting hydrogen bonding because if no H is connected to a Fluorine, Oxygen, or/and Nitrogen then it is not H Bond even if H and one of the elements of FON is in the Chemical Equation.) INTERmolecular forces H bonding is ____________ ______________ force strongest INTERmolecular force What is the following list of?
- kj/mole 400, Covalent Single Bond, C-C
- kj/mole 600, Covalent Double Bond, C=C
- kj/mole 800, Covalent Triple Bond, C Ī C INTRAmolecular forces Ionic bonds also increase with increasing _______ density charge (Recall 1, 2, 3 skip, 3, 2, 1 method on periodic table) Which of the following molecules have the largest intermolecular and intramolecular forces, respectively? C2H5OH, C2H4, C2H2, CHCl
- C2H2, C2H
- CHCl3, C2H
- C2H5OH, CHCl
- C2H5OH, C2H
- C2H5OH, C2H Which of the following compounds are likely to form intramolecular bonds that exceed 500 kJ/mole? a)NaCl, Cl b)N2, CaO c)CaO, CCl d)CH4, N b)N2, CaO Which of the following is the strongest intermolecular force? a)Ionic bonding b)Hydrogen bonding c)Dipole-dipole d)Dispersive forces b)Hydrogen bonding Intermolecular force theory (dispersive forces and permanent dipoles)
ā¢Dispersion forces occur from the instantaneous dipoles formed by asymmetrically distributed electrons. ā¢Dispersion occurs in all compounds but is the dominant force in non-polar (symmetrical) molecules. As molecules increase in size, dispersion forces can grow to allow liquids and solids to be formed. ā¢Dipole-dipole interactions occur in molecules that have permanent dipoles (polar compounds). The magnitude of these forces is related to the size of the permanent dipoleā ĪEN. The attractions between the positive and negative ends of permanent dipoles are dipole-dipole forces The momentary attractions between the positive and negative ends of temporary dipoles are dispersion forces Polar Molecules have permanent dipoles - > dipole-dipole forces (dominant) AND dispersion forces Nonpolar Molecules have instantaneous dipoles - > dispersion forces only Instantaneous Dipoles (Dispersion Forces) vs Permanent Dipoles (Dipole-dipole and H-bonding) Dispersion (London) forces result from.. 1.The formation of a loose covalent linkage between a hydrogen atom connected to a very electronegative atom in a neighboring molecule. 2.Distortion of the electron cloud of an atom or molecule by the presence of nearby atoms or molecules 3.Attraction between molecules in a liquid and molecules or atoms in a solid surface with which the liquid is in contact. 4.Attractive forces between a molecule at the surface of the liquid and those beneath it which are not balanced by corresponding forces from above. 5.The balance of attractive and repulsive forces between two polar molecules. 2.Distortion of the electron cloud of an atom or molecule by the presence of nearby atoms or molecules Which of the following statements about intermolecular forces is correct? a)Polar compounds are not able to form instantaneous dipoles b)Compounds exhibiting only dispersion forces are not able to form solids c)Dispersion forces are formed by the creation of instantaneous dipoles in otherwise nonpolar molecules d)Permanent dipoles form only in molecules with symmetrical geometries c)Dispersion forces are formed by the creation of instantaneous dipoles in otherwise nonpolar molecules H bonding looking at the graph ā¢Note the normal linear relationship between size of compound and IMF. As shell increases, # of e- increases, and IMF increases
d) instantaneous dipoles 1.a, c, c, d, b 2.c, d, a, a, b 3.a, b, c, b, a 4.a, b, d, a, c 5.a, d, c, a, b 6.c, b, d, c, c 7.b, d, c, d, d 5.a, d, c, a, b Identify the kinds of intermolecular forces that might arise between molecules of CH3OH. a)Dispersion forces and dipole-dipole b)Hydrogen bonding only c)Dipole-dipole and hydrogen bonding d)Dispersion forces, dipole-dipole, and hydrogen bonding d)Dispersion forces, dipole-dipole, and hydrogen bonding To assign IMF of different molecules use the graphic that asks yes or no questions to help guide you to find what is the most dominant force in each different molecule For which molecule below are dipole-dipole interactions likely to make the most significant contribution to intermolecular forces?a)BH b)CH3Cl c)H2O d)NH b)CH3Cl Identify the dominant intermolecular force in the following species, respectively: RbCl, C6H6(benzene), HI, Fe2O3, CH2NH. I)Ionic forces II)Hydrogen bonding III)Dipole-dipole IV)Instantaneous dipoles a)I, IV, III, I, II b)III, IV, I, I, II c)I, III, III, IV, II d)I, II, IV, I, III a)I, IV, III, I, II Which IMF is in all molecules? a) Van der Waals
b) Dipole-Dipole c) Ion-Dipole d) hydrogen bonding a) Van der Waals (another word for dispersion) The following definitions are properties of what? Boiling Point: A bulk phenomenon in which gas bubbles from the vapor of the liquid form and the escape became the vapor pressure of bubble > atm. pressure Surface Tension: A surface phenomenon in which an inward force reduces the surface area of liquid. This is why liquids like H2O bead up on windrows in the rain. Capillary Action: Surface phenomenon in which the liquid climbs the walls of the container because of IMF. Viscosity: The tendency of a liquid to resist pouring because of IMF attraction to bulk solution. ĪHvap: The energy in IMF that must be overcome for a liquid on the surface to vaporize. Vapor Pressure: The pressure of the vapor above the surface and is inversely related to IMF Evaporation Rate:How quickly a liquid will vaporize. Increases at IMF decreases. physical properties of liquids Surface tension describes
- The inward forces that must be overcome in order to expand the surface area of a liquid.
- The forces of attraction between surface molecules of a solvent and the solute molecules.
- Adhesive forces between molecules. 4.The forces of attraction between the surface of a liquid and the air above it
- The inward forces that must be overcome in order to expand the surface area of a liquid. During vaporization of water which of the following statements is NOT true? a)Intramolecular bonds are broken during the vaporization process b)Boiling involves the disruption of hydrogen bonds c)The bubbles that form before the water reaches its boiling point are primarily air d)Boiling is the phase transition between liquid and gas a)Intramolecular bonds are broken during the vaporization process Ranking properties of liquids (direct relationship with IMF)
- first sort the molecules into the IMF buckets in the order of Dispersion < Dipole-dipole < H-Bond < Ionic
- Sort them in order based in the certain bucket/type of IMF. Dispersion: as MW increases, dispersion increases ( Ex: H2O < O2 < SF6 )
c)C4H8 at 30Ā°C d)C4H8 at 50Ā°C a)C8H18 at 30Ā° (Recall if you cool honey it will be more viscous/high viscosity) Rank the following compounds by boiling point, from lowest to highest: HF, CH3F, H2O, NH3.
- CH3F < NH3 < HF < H2O
- HF < H2O < CH3F < NH
- H2O < CH3F < NH3 < HF
- H2O < NH3< CH3F < HF
- CH3F < NH3 < HF < H2O Rank the following species by vapor pressure from lowest to highest:K2S, CHCl3, Kr, CH3NH2, CHF 1.CH3NH2 < CHF3 < K2S < CHCl3 < Kr 2.CH3NH2< CHCl3 < CHF3 < Kr < K2S 3.Kr < CH3NH2< CHF3 < CHCl3 < K2S 4.K2S < CH3NH2< CHF3 < CHCl3 < Kr 4.K2S < CH3NH2< CHF3 < CHCl3 < Kr Assigning types of solids 1.Solidsthat are metals. Elements found down and to the left on table. Ex: Fe, Pb, Na. 2.Solids that are ionic: Combination of metal cation and nonmetal anion to make a salt. Ex: NaCl, CaO 3.Solids that are covalent network. Found on right side of table. Long chains of covalent bonded atoms: diamond, cellulose, graphite 4.Molecular solids.Solids from IMF forming at low temperature. These are the molecules you drew in unit 2 that have frozen Frozen H2O Frozen CO Have covalent bonds but are small molecules Arrange Al2O3, Nb, I2, C (s) (diamond) In the order metallic solid, covalent network, covalent solid, ionic solid.
- Nb; C (s) diamond; I2; Al2O
- Al2O3; C (s) (diamond); I2; Nb
- C (s) (diamond); Nb; Al2O3; I
- Nb; I2; C (s) (diamond); Al2O
- Nb; C (s) diamond; I2; Al2O Which of the following is not a covalent network solid? a)glass b)diamond
c)table sugar d)cellulose c) table sugar Methane (CH4) forms a molecular solid. What type of forces hold it in a solid configuration? I)London forces (Dispersion) II)Dipole-dipole forces III)Hydrogen bonding a)II and III only b)II only c)I, II, and III d)I only d)I only Melting point is _________ related to IMFs directly Note* See ranking IMFs Flashcards to see how to rank/sort them it the same process as another directly related property. Most important thing is in ranking salts and their ________ _______. These are based on _______ _______:+1 - 1+2 - 1+2 - 2NaCl < CaCl2 < CaO melting point, charge density Put the following compounds LiF, HF, F2, NF In order of increasing melting points. 1.LiF, HF, F2, NF 2.NF3, F2, HF, LiF 3.F2, HF, NF3, LiF 4.LiF, NF3HF, F 5.LiF, HF, NF3 , F 6.NF3, HF, F2 , LiF 7.F2, NF3, HF, LiF 8.LiF, F2, HF, NF 7.F2, NF3, HF, LiF
