Chapter 12 - Molecular Nature of Matter and Change
For a simple cubic there is _ atom at each corner
1/8 1/8 atoms at 8 corners = 1 atom/unit cell
Which of the factors contributes to a low viscosity of a liquid? A) high boiling point B) hydrogen bonding C) compact molecular shape D) low temperature E) high molar mass
?
Viscosity
A liquid's resistance to flowing
Which of the following has the lowest boiling point? A) C₅H₁₂ B) C₇H₁₆ C) C₉H₂₀ D) C₁₁H₂₄ E) C₁₃H₂₈
A) C5H12 The compound with weaker intermolecular forces will have lower bp.
Which one of the following would have the highest heat of vaporization? A) CH₃OH B) CH₂F₂ C) NF₃ D) CHF₃
A) CH3OH
Ammonia and hydrogen fluoride both have unusually high boiling points due to _____ A) dispersion forces. B) dipole-dipole interactions. C) hydrogen bonding. D) ion-dipole interactions. E) low molar masses.
C) Hydrogen bonding Both ammonia and HF contain H- atom , that is directly bonded to one of the highly electronegative atoms like F,N,O etc. ,so their high boiling point is due to H- bonding.
When the temperature of a liquid increases what happens to the viscosity and surface tension of the liquid? A) Viscosity increases, surface tension increases. B) Viscosity increases, surface tension decreases. C) Viscosity decreases, surface tension decreases. D) Viscosity decreases, surface tension increases.
C) Viscosity decreases, surface tension decreases.
Which property typically indicates strong intermolecular forces are present in a liquid? A) low heat of vaporization B) low critical temperature C) low vapor pressure D) low boiling point E) low melting point
C) low vapor pressure Of these options, only a low vapor pressure indicates strong intermolecular forces, as it implies that the liquid molecules are less likely to exit into the vapor (gas) phase
Based on intramolecular forces, which of the following is predicted to have the highest boiling point? A. CH4 B. CH3Cl C. CH3OH D. C2H6
C. CH3OH Higher intermolecular forces generally result in higher boiling points because it takes more energy to overcome these forces and transition from the liquid phase to the gas phase.
Which of the following exhibits dipole-dipole intermolecular forces in a pure substance? A. BF3 B. CO2 C. NH3 D. Br2 E. CF4
C. NH3 Dipole-dipole forces - Exhibited by any system that contain polar compounds. Draw a molecular structure of the options & you may see that the NH3 has a net dipole moment. (all other options are non-polar molecules)
What are exothermic phase changes?
Condensation, freezing, and deposition - Energy is released as the molecules get closer and attract each other.
Consider the intermolecular forces present in a pure sample of each of the following compounds: CH₃CH₂CH₂CH₃ and CH₃CH₂CH₂OH. Identify the intermolecular forces that these compounds have in common.
Dispersion forces only. The first pure sample is a nonpolar bond and does not meet hydrogen bonding requirements
Induced Dipoles
Distortion in the electron cloud Ex: O-O + The cloud that is around the O2 will be pulled toward the + charge hence distorting the electron cloud. (from an outside force, in this case + charge)
What is established between vaporization and condensation?
Dynamic equilibrium - the rate of vaporization equals the rate of condensation.
Which of the following substances would have the greatest dispersion forces? A. H2 B. O2 C. Cl2 D. Br2 E. I2
E. I2 Dispersion forces - Arise from instantaneous changes in electron density Compounds that have more electrons(molecular weight) will have a greater dispersion force.
What is Kinetic Energy
Energy of motion of partials - Speed of molecules/atoms is proportional to absolute Temperature.
Heat of Vaporization
Enthalpy change for the conversion of 1 mol of a liquid to gas
Heat of fusion
Enthalpy change for the conversion of 1 mol of a solid to a liquid
Heat of sublimation
Enthalpy change for the conversion of 1 mol of a solid to gas
Polarizability
Of a particle is the ease with which its electron cloud is distorted. - The bigger the electron cloud, the easier it is influenced to be distorted. - Increases with increasing number of electrons & Molar mass
What is Critical point?
The end of the liquid/gas phase boundary. - High pressure & Temp - The densities of the liquid and gas phases become equal
Surface tension
The energy needed to increase the surface area of a liquid by a unit amount. (Unites: J/m2)
B) Body Centered Cubic
What type of packing is shown in this unit cell? A) Simple Cubic B) Body Centered Cubic C) Face Centered Cubic D) Hexagonal Closest Packed
Intermolecular Forces
(IMF) Interparticle forces Potential Energy
What are 3 weaker Intermolecular forces and liquid properties
- Viscosity decreases - Adhesive Forces are stronger; more concave behavior in a capillary - Surface tension decreases
What are 3 Stronger Intermolecular forces and liquid properties
- Viscosity increases - Cohesive forces are stronger; more convex behavior in a capillary - Surface Tension Increases
Which one of the following correctly ranks the compounds in order of lowest vapor pressure to highest vapor pressure based only in intermolecular forces? A) CH₃CH₂OH < CH₃OCH₃ < CH₃CH₂CH₃ B) CH₃OCH₃ < CH₃CH₂CH₃ < CH₃CH₂OH C) CH₃CH₂CH₃ < CH₃CH₂OH < CH₃OCH₃ D) CH₃CH₂CH₃ < CH₃OCH₃ < CH₃CH₂OH
A) CH₃CH₂OH < CH₃OCH₃ < CH₃CH₂CH₃ Lowest vapor pressure to Highest vapor pressure CH₃CH₂OH will be harder to create vapor pressure compared to CH₃CH₂CH₃
Which of the following should exhibit the highest viscosity at 298 K? A) HOCH₂CH₂OH B) CH₃OCH₃ C) CH₃OH D) CH₃Br E) CH₂Cl₂
A) HOCH₂CH₂OH High Viscosity is like syrup Low viscosity is like water. Higher intermolecular forces have high viscosity.
Which best explains why the trend in noble gas boiling points increases down the group? A) increasing dispersion interactions B) increasing dipole-dipole interactions C) increasing ion-dipole interactions D) increasing hydrogen bonding interactions E) increasing ion-ion interactions
A) increasing dispersion interactions Higher boiling points are from stronger intermolecular forces. The strength of dispersion forces increases with a greater number of electrons, therefore as you go down the group of noble gases, the number of electrons in each atom increases. Hence, leading to an increase in dispersion forces and therefore an increase in bp
Dipole-dipole interactions
Are the attractive forces between the permanent dipoles of two polar molecules.
Intermolecular forces
Arise from the attraction between molecules with partial charges, or between ions and molecules. - weak compared to bonding forces because they involve smaller charges that are farther apart *Stronger intermolecular forces lead to Tb lower Pv values.*
Based on intermolecular forces, which of the following would you expect to have the highest boiling point? A) H₂ B) NH₃ C) N₂ D) CH₄
B) NH3 Hydrogen bonding is the strongest intermolecular force. Hence, the highest bp
Which of the following substances is a liquid at room temperature? A. CH3CH3 B. CH3OH C. CH4 D. HCl E. CF4
B. CH4OH - You must look at the given substances boiling points to be able to understand which would be a liquid at room temperature.
Which one of the following correctly ranks the compounds in order of lowest enthalpy of vaporization to highest enthalpy of vaporization based only in intermolecular forces? A) CH₃NH₂ < CH₃SH < CH₃CH₃ B) CH₃NH₂ < CH₃CH₃ < CH₃SH C) CH₃CH₃ < CH₃SH < CH₃NH₂ D) CH₃SH < CH₃NH₂ < CH₃CH₃
C) CH₃CH₃ < CH₃SH < CH₃NH₂
Rank the following compounds in order of lowest boiling point to highest boiling point based on intermolecular forces. A) HF < HCl < HBr < HI B) HI < HBr < HCl < HF C) HCl < HBr < HI < HF D) HBr < HI < HF < HCl
C) HCl < HBr < HI < HF
For this correct answer, Both molecules experience dispersion forces and both have polar bonds. (c-cl) and (c-o)
Consider the intermolecular forces present in a pure sample of each of the compounds shown below. Identify the intermolecular forces that these compounds have in common. A. Dispersion forces only B. Dipole-dipole forces only C. Dispersion forces, dipole-dipole forces, and hydrogen bonding. D. Dispersion forces and dipole-dipole forces.
Condensation
Conversion from gas to liquid
Deposition
Conversion from gas to solid
Vaporization
Conversion from liquid to gas
Freezing
Conversion from liquid to solid
Sublimation
Conversion from solid to gas
Melting (fusion)
Conversion from solid to liquid
All _ _ exhibit London dispersion forces.
Covalent compounds
What is a type of long-ranged order?
Crystal lattice - A system of point defining the geometric pattern of the crystal
How much of an atom on the corner of a cubic unit cell is contained inside the unit cell? A) 1 atom B) 1/2 of an atom C) 1/4 of an atom D) 1/8 of an atom
D) 1/8 of an atom
Consider the intermolecular forces present in a pure sample of each of the following compounds: CH₃CH₂CH₂CH₂F and CH₃CH₂OCH₂CH₃. Identify the intermolecular forces that these compounds have in common. A. Dispersion forces only B. Dipole-dipole forces only C. Dispersion forces, dipole-dipole forces, and hydrogen bonding D. Dispersion forces and dipole-dipole forces
D. Dispersion forces and dipole-dipole forces This cannot be a hydrogen bond because if drawing out the structure, both O and F are connected to a carbon, not hydrogen. Therefore all molecules will have dispersion forces, and both molecules are polar.
Dipole-induced dipole
Dipole charged - polarizable charge
In a pure sample of NO₂, what forces of attraction exist between the molecules?
Dipole-Dipole and Dispersion forces
Consider the intermolecular forces present in a pure sample of each of the following compounds: CH₃CH₂OCH₂CH₃ and CH₃CH₂CH₂CH₃. Identify the intermolecular forces that these compounds have in common.
Dispersion forces only
London dispersion forces
Very weak interactions due to the momentary changes in electron density in a molecule.
Intramolecular Forces
Forces are found within a molecule, the chemical behavior of each phase of matter is the same because the same basic particles is present in each case. forces are found between molecules. Potential energy
Convex meniscus
Forces between liquid to liquid (cohesive) are stronger than liquid to wall
Concave meniscus
Forces between walls and liquid are stronger (adhesive) than those between liquid molecules
What is simple cubic?
Has an atom on each corner
What is a face-centered cubic?
Has atom on corners and every face of the cell
What is a body-centered cubic?
Has atoms on corners and the center of the cell
Viscosity _ with increasing _
Viscosity decreases with increasing temperature
As a pure substance, which of the following could experience dipole-dipole interactions? I. CO₂ II. HCl III. CCl₄
II. HCl CO2 - is a linear symmetrical molecule (nonpolar) CCl4 is a symmetrical tetrahedral molecule (nonpolar) HCl is a linear asymmetrical molecule that is polar
Hydrogen bonding
Occurs when a hydrogen atom bonded to O, N, or F is electrostatically attracted to an O, N, or F atom in another molecule. Ex: H2O - H2O - Is the strongest of the three types of intermolecular forces.
What are Ion-Induced dipole?
Ion charged polarizable charge
What is an ion-dipole?
Ion-charged dipole charge
Which of the following is predicted to have the lowest boiling point? A) I₂ B) CS₂ C) CCl₄ D) CBr₄
Low bp is due to weak intermolecular forces, I was able to determine which was the weakest by determining the molecular mass of each option.
What is Lattice points?
Points with identical surroundings (can be occupied by atoms, ions, or molecules)
What is critical pressure (Pc)
Pressure at the critical point.
Intramolecular forces are ___
STRONG.
Vapor Pressure (Pv) Increases with increasing ___
Temperature. A molecule must have enough KE to escape the liquid in order to vaporize. With a high temp the Vapor pressure will be high.
The change in electron density creates a ___
Temporary dipole. - The weak interaction between these temporary dipoles constitutes London dispersion forces.
What is critical temperature (Tc)
Vapors can't be liquified at any pressure if temperature is greater than Tc.
The _ the molecule, the larger the attractive force, and the stronger the _ _
The larger the molecule, the larger the attractive force, and the stronger the intermolecular forces.
Vapor Pressure (Pv)
The pressure exerted by the vapors over a liquid at equilibrium. - Pv Increases with decreasing strength of intermolecular forces. Weaker forces -> Higher Pv Stronger forces -> Lower Pv
What is Triple Point?
Three phases in equilibrium
What is an identical repeating unit?
Unit cell - The smallest set of lattice points sufficient to reproduce the entire lattice
What are endothermic phase changes?
Vaporization, melting, sublimation - Energy must be absorbed to overcome the attractive intermolecular forces
