Intermolecular Forces and Colligative Properties (CHAPTER 18)

Intermolecular Forces

Attraction between molecules of the same type

Dispersion Forces

Weakest IMF arising from instantaneous dipoles

Dipole-Induced Dipole Forces

Polar molecules polarizing nonpolar ones

Dipole-Dipole Forces

Occurs in molecules with uneven electron distribution

Hydrogen Bonding

Strong dipole force with H bonded to F, O, or N

Ion-Dipole Forces

Attraction between ions and polar molecules

Boiling Point of Ethane

-88.0 ºC, easier to boil

Polarizability

Ease of electron cloud distortion by neighboring charges

Surface Area Impact on Boiling Points

Flat/rod-shaped > spherical molecules of same mass

n-Pentane vs. Neopentane Boiling Points

n-Pentane (36.1 ºC) vs. Neopentane (9.5 ºC)

Viscosity

Resistance of a liquid to flow

Cohesion

Forces binding molecules in a liquid

Surface Tension

Energy to increase surface area, affected by IMFs and temperature

Adhesion

Forces allowing liquid-surface interaction

Capillary Action

Liquid flow against gravity in a thin tube

Vaporization

Phase change from solid/liquid to gas

Evaporation

Surface liquid changing to gas at T < Tbp

Enthalpy of Vaporization

Heat to vaporize one mole of liquid

Heating/Cooling Curves

Energy in phase change and temp change

Volatile Substances

Liquids evaporating easily due to weak IMFs

Nonvolatile Substances

Liquids not evaporating easily due to strong IMFs

Boiling Point Vocabulary

Tbp: Pvap = Patm, Normal BP: Tbp at P = 1 atm, Standard BP: Tbp at P = 1 bar

Clausius-Clapeyron Equation

Relates vapor pressure and temperature

Solubility

Ability of a substance to dissolve in a solvent

Miscibility

Extent of substance dissolution in a particular solvent

Miscible

Liquid solutes that can be dissolved in other liquids.

Immiscible

Liquids that cannot be mixed to form a homogenous solution.

Solubilities of Alcohols

Table showing solubility of alcohols in water and hexane.

Henry's Law

The solubility of a gas is directly proportional to its partial pressure above the solution.

Henry's Law Constant

Constant (kH) specific to gas, solvent, and temperature.

Molarity

Concentration unit expressing moles of solute per volume of solution.

Molality

Concentration unit expressing moles of solute per mass of solvent.

Colligative Properties

Properties of a solution altered by solute particles, like boiling point elevation and freezing point depression.

Electrolytes

Solutes breaking up into ions in solution.

Nonelectrolytes

Solutes remaining as whole molecules in solution.

Van't Hoff Factor

Number of ions a solute breaks up into in solution.

Freezing Point Depression

Disruption of intermolecular forces by solute particles, lowering freezing point.

Boiling Point Elevation

Solute particles affecting the boiling point of the solvent.

Vapor Pressure

Pressure exerted by particles that escape from a liquid to form a vapor.

Van't Hoff factor

Theoretical factor counted as an exact number in sig figs

Normal boiling point

Boiling point with 100.00 ºC plus 3.07 ºC

Vapor pressure reduction

Decrease in vapor pressure due to nonvolatile solute

Raoult's Law

Equation stating partial vapor pressures in ideal liquid mixtures

Mole fraction

Ratio of moles of a component to total moles in a mixture

Osmosis

Solvent flow through a semipermeable membrane

Osmotic pressure

Pressure needed to stop osmotic flow

Raoult's Law deviations

Changes due to solute-solvent interactions deviating from Raoult's Law

Endothermic

Absorbing heat or energy during a process

Heats of fusion and vaporization

Energy absorbed/released during phase changes

Supercritical fluid

State above critical point, filling container like a liquid

Phase diagram

Graph showing states of matter under different conditions

Molality of solution

Total concentration of solutes in a solution

Total vapor pressure

Sum of partial pressures of volatile components in a solution

Mole fraction of pentane

Ratio of moles of pentane to total moles in a solution vapor

Colligative properties

Properties dependent on the number of solute particles in a solution

Heat of vaporization

Energy required to convert a liquid to vapor at a constant temperature