Chapter 10

Question 1

Intramolecular vs. Intermolecular forces

Answer 1

• Intramolecular forces: interactions btwn e- pairs(atoms) within a molecule
  
  • both electrostatic in nature
  • hundreds to thousands of kj/mol
• Intermolecular forces: forces btwnmolecules and btwn molecules and ions
  
  • weaker than intra
  • <1-100 kj/mol

Question 2

Attractive forces and states of matter

Answer 2

• The stronger the attractiveforcesamong the particles in a solid, the greater the amount of energy needed to overcome those forces to cause melting or vaporization.
• As atomic inc., bp inc.

Question 3

Dispersion Forces/ London force

Answer 3

• an intermolecular force btwn nonpolar molecules caused by the presence of temporary dipoles in the molecule.
• dispersion forces btwn small atoms or molecules are weak , but large molecules have a large # of these interactions that dominate a smaller # of strong interactions in a system.
• weakest
• found in ALL molecs

Question 4

induced dipole

Answer 4

• the separation of charge produced in an atom or molecule by a momentary uneven distribution of e-
• caused when one atom’s positive nucleus is attracted To the other atom’s negative e - and vice versa, even as their e - clouds repel each other the competing interactions can causethe electrons around each atom to be distributed unevenly producing temporary induced dipoles of partial electric charge that are attracted to regions of opposite partial charge on the adjacent atom .

Question 5

polarizability

Answer 5

• the relative ease with which the electron cloud in a molecules in, or atom can be distorted, inducing atemporary dipole.
• The larger the cloud of electrons surrounding a nucleus in an atom or several nuclei in a molecule, the more likely those electrons are to be distributed unevenly , or polarized.
• greater polarizability = stronger temporary dipoles and stronger intermolecular interactionS.
  
  • large molec = more polarizable = stronger dispersion = higher MP and BP

Question 6

ion-dipole interactions

Answer 6

• an attractive force btwn an ion and a molecule that has a permanent dipole moment(Ex:water) .
  
  • Na CI dissolves in water because Na and CI ions interact w/ the permanent dipoles of the polar water molecules.
• As an ion is pulled away from its solid state neighbors , it becomes surrounded by water molecules forming a sphere of hydration.

Question 7

sphere of hydration

Answer 7

• the cluster of water molecules surrounding an ion in aqueous solution
  
  • general term for any solvent is sphere of solvation

Question 8

dipole-dipole interaction

Answer 8

• an attractive force btwn. polar molecules
  
  • have permanent dipole moments
• experienced by water molecules further from the ions bcause theyare more randomly oriented than those in the inner hydration sphere
• only involve partial charges so they’re not as Strong as ion-dipole

Question 9

dipole-induced dipole interaction

Answer 9

• an attraction btwn a polar molecule and the oppositely charged pole it temporarily induces in another molecule.
  
  • polarizability determines magnitude

Question 10

hydrogen bonding

Answer 10

• strongest dipole dipole interaction
• occurs btwn H atom bonded to a small, highly EN element (FON) and an O or N atom in another molecule.
• Molecules of HF also form hbonds
  
  • play a huge role in DNA + allow protein folding

Question 11

rank from strongest to weakest : dipole dipole, dispersion , ion-dipole , h-bonding , dipole-induced dipole

Answer 11

Question 12

like dissolves like

Answer 12

• ionic compounds dissolve in polar solvents b/c of strong ion-dipole interactions
  
  • polar solutes dissolve in polar solvents b/c of dipole-dipole interactions btwn solute and solvent molecules
• Nonpolar solutes tend not to dissolve in polar solvents because the solvent– solute interactions that promote dissolution are weaker than the solute–solute interactions that keep solute molecules together and the solvent–solvent interactions that keep solvent molecules together

Question 13

ether

Answer 13

• organic compound with the general formula R-O-R
  
  • R is any alkyl group or aromatic ring
    
    • 2 R groups can be different

Question 14

factors that influence solubility

Answer 14

• polarity
• temperature
• pressure
• attractive forces

Question 15

hydrophobic

Answer 15

• a “Water fearing” or repulsive interaction between a solute and water that diminishes water solubility
  
  • Ex: nonpolar interactions like dispersion forces between hydrocarbon chains

Question 16

hydrophilic

Answer 16

• a “water loving” or attractive interaction btwn a solute and water that promotes water solubility
  
  • When molecules contain both polar and nonpolar groups, as alcohols do, solubility in water is due to the balance btwn. hydrophilic thydrophobic interactions
    
    • As the hydrophobic portion of the molecule increases in size , the entire molecule becomes more hydrophobic and solubility in water Decreases.

Question 17

solubility of O2 in water

Answer 17

• due to relatively weak dipole-induced dipole interactions btwn water molecules + the nonpolar molecules of O 2 gas make O2 gas soluble (or any sparingly soluble gas) in water .
• As temp increases, solubility of gases decreases
  
  • this is why fish rise to surface of ponds in summer
  • as temp increases, KE of molec increases, and more energy is available to disrupt intermolecular attractions ~ reducing solubility.
• As pressure decreases, solubility of gases decreases
  
  • why we hear rush of escaping gas when opening a bottle of carbonated beverage
  • the more collisions, the more gas molecules that may form in form intermolecular attractions w/ the solvent
    
    • more pressure = more soluble

Question 18

Henry’s Law

Answer 18

• C_gas=k_HP_gas
• the principle that the concentration of a sparingly soluble , chemically unreactive gas in a liquid is proportional to the partial pressure of the gas.

Question 19

Vapor pressure of pure liquids

Answer 19

• The rate at which the molecules make the transformation from liquid to gas depends on :
  
  • Temperature: higher temp =higher # of molecules w/ enough KE to break the attractive forces that hold them together in the liquid and to enter the gas phase
  • Surface area: higher SA of liquid = greater # of molecules on the surface in a position toenter the gas phase
  • Intermolecular forces : stronger IMF = a greater KE required for a molecule to escape the surface, and a smaller # of molecules in the population that have this energy

Question 20

vapor pressure

Answer 20

• the pressure exerted by a gas at a given temp in equilibrium w/ its liquid phase
  
  • occurs during dynamic equilibrium at constant temp.

Question 21

normal boiling point

Answer 21

• the temp at whichthe vapor pressure of a liquid = 1 atm (760 torr)
  
  • at some point as temp increases , the vapor pressure will reach 1 atm

Question 22

Clausius - Clapeyron equation

Answer 22

• a relation ship btwn the vapor pressure of a substance at two temperatures and its heat of vaporization
• volatile evaporates readily at normal temps and pressures
  
  • at a given temp, a more volatile substance has a highervapor pressure than a less volatile substance
  • As temp increases, vapor pressure increases

Question 23

phase diagram

Answer 23

• a graphical representation of how the stabilities of the physical states of a substance depend on temp + pressure .

Question 24

Surface tension

Answer 24

• the resistance of a liquid to any increase in its SA.
• represents the energy needed to separate the molecules at the surface of a liquid .

Question 25

meniscus

Answer 25

* the Concave or convex surface of a liquid in a small diameter tube. * a result of cohesive forces which are interactions btwn like particles, and adhesive forces which areinteractions btwn unlike particles *

Question 26

capillary action

Answer 26

* the rise of a liquid in a narrow tube as a result of adhesive forces btwn the liquid and the tube and cohesive forces within the liquid * the water column reaches its max height when the downward force of gravity balances the upward adhesive and cohesive forces.

Question 27

Viscosity

Answer 27

* the resistance to flow of a liquid * influenced by IMF * In nonpolar compounds , increase in molar mass = increase in viscosity * larger molar mass = stronger dispersion forcesso larger molecules do not flow as easily when poured . * We predict that octanol has a higher viscosity than ethanol, reflecting the greater dispersion forces in octanol. * Water is more viscous than gasoline even though water molecules are much smaller than the nonpolar molecules in gasoline. The remarkable viscosity of water is another property directly related to the hydrogen bonds between water molecules. * Another property unique to water is how its density changes with temperature