CHY 122 - Chapter 11: Liquids and Intermolecular Forces

intermolecular forces

exist between molecules

intramolecular

covalent bonds within one molecule

intermolecular

between 2 different molecules

gases

KE_avg » IMF

liquid

KE_avg ~ IMF

solid

KE_avg « IMF

dispersion

all atoms/molecules (largest section of the pyramid)

dipole-dipole

form between polar molecules when net dipoles align with or against each other (second largest section of the pyramid)

hydrogen bonding (10-40 kJ/mol)

an attraction between H bound to O, N, or F and an electronegative atom in a nearby molecule (third largest section of the pyramid)

ion dipole (>50 kJ/mol)

exist between an ion and a polar molecule (typically H₂O (smallest section of the pyramid)

dispersion forces (0.1 - 30 kJ/mol)

motion of electrons in an atom or molecule can create a temporary or induced dipole moment

dipole moment

separation of charge

polarizability

the ease with which charge can be distorted (squishiness of e^- cloud)

dipole-dipole interactions

occur in addition to dispersion forces and are stronger than repulsive forces

effects of mass

as mass increases, molecules increase in size and electrons are easier to distort

effects of structure

as surface area increases, more interactions are possible between molecules

nonpolar covalent bonds

equal electron sharing

polar covalent bonds

unequal electron sharing

electronegativity

the ability of an atom in a molecule to attract electrons itself

polarity of molecules

molecular polarity arises when bond dipoles do not cancel each other out

intermolecular interactions

1. intermolecular forces are additive

2. dispersion forces are approximately equal for two compounds with comparable MM and surface area

3. for compounds without hydrogen bonding, dispersion forces usually determine overall IMF strength

viscosity

resistance of a liquid to flow

phase changes

require a change in the energy of the system and are additive

solid to liquid

melting, ΔH_fusion

liquid to solid

freezing, -ΔH_fusion

liquid to gas

evaporation, ΔH_vaporization

gas to liquid

condensation, -ΔH_vaporization

solid to gas

sublimation, ΔH_sublimation

gas to solid

deposition, -ΔH_sublimation

heating curve

graph of temperature vs. amount of heat added

normal boiling point

where pressure is 1 atm

plateau

making or breaking intermolecular forces (temperature is constant)

ramped

energy used to change temperature (no phase changes)

vapor pressure

the pressure exerted by a vapor when the liquid and vapor are in dynamic equilibrium

equilibrium

opposite processes or reaction occur at the same rate

open system

vapor escapes, no vapor pressure

closed system

vapor trapped, applies pressure to surface of remaining liquid (more vapor molecules = more vapor pressure)

inversely proportional

vapor pressure and intermolecular forces

more volatile

high vapor pressure

volatile

easily vaporizes

triple point

all phases in equilibrium on a phase diagram

critical temperature

highest temperature at which the liquid phase can form

critical pressure

the pressure required to bring about liquefaction at the critical temperature

supercritical fluid

occurs when the critical temperature and pressure are exceeded making the liquid and gas phases indistinguishable

phase diagrams

can determine phase of matter at STP

left curving liquid line

liquid more dense than solid

right curving liquid line

solid phase more dense than liquid