Chapter 11: Liquids, Solids, and Intermolecular Forces Flashcards
Coulomb’s law
Potential energy (E) and distance (r) are inversely related
E decreases (becomes more negative) as r decreases
Potential energy and product of charges are directly related
E decreases as q1q2 decreases (becomes more negative)
*q1 and q2 are of opposite signs (charges)
Effect of intermolecular forces on boiling and melting points
High intermolecular forces = high boiling/melting point
Dispersion force
Result of fluctuations in the electron distribution within molecules or atoms
Depends on fleeting charge separation called instantaneous or temporary dipole
Stronger dispersion force:
Higher molar mass (polarizability)
More surface area (longer chains)
Instantaneous/temporary dipole
Associated with dispersion force
When an atom or molecule displays polarity temporarily (as electrons are constantly moving and bond to be dense on one end)
Permanent dipole
Characteristic of a polar molecule where positive and negative ends can interact with opposite ends of other like molecules
Associated with dipole-dipole force
Miscibility
Ability to mix without separting into two states
“Like dissolves like”
*Oil and water are immiscible
Hydrogen bond
Occurs when N, O, or F are bonded directly to a hydrogen
Special kind of dipole-dipole force where H has the partial positive charge and F, O, or N has the partial negative charge
Ion-dipole forces
Present only in mixtures of substances (ionic + polar)
Strengths of intermolecular forces
Dispersion < Dipole-dipole < H-bonding < Ion-dipole
Surface tension
Energy required to increase the surface area of a liquid by a unit amount
Molecules on surface are strongly attracted by interior molecules
Higher surface tension = greater intermolecular forces
Temperature increases –> surface tension decreases
Viscosity
Liquid’s resistance to flow
Higher viscosity = stronger intermolecular forces
More spherical molecules = less viscous
(Chains are more viscous)
Temperature increases –> viscosity decreases
Capillary action
The ability of a liquid to flow (“climb” up a thin tube against influence of gravity
Depends on two forces:
Cohesion
Adhesion
The stronger the cohesion (intermolecular forces), the smaller the capillary action
Cohesive forces
Forces that hold liquid molecules together
Adhesive forces
Forces that attract the outer liquid molecules to tube’s surface
Vaporization
AKA evaporation
Escape of molecules from liquid to gas phase - endothermic
Kinetic energies vary within liquid body
Molecules on surface have higher kinetic energies and more easily overcome intermolecular forces
Affected by:
Temperature
Surface area
Intermolecular forces (volatility)
Condensation
Molecules transition from gas to liquid phase - exothermic
Some molecules lose energy through collisions and liquid [re]captures them
Dynamic equilibrium
Occurs when two opposite processes reach the same rate so that there is no net gain or loss of material
Rate of evaporation = constant
Rate of condensation = increases until met with rate of evap
Vapor pressure
Pressure exerted by a vapor when it is in dynamic equilibrium with its liquid
Quantity & surface area = negligible
Vapor pressure increases with temperature and with decreasing strength of intermolecular forces
Heat (enthalpy of vaporation)
ΔHvap = -ΔHcondensation
The amount of heat energy required to vaporize one mole of a liquid
kJ/mol
Somewhat temperature dependent
Boiling point
Temperature at which vapor pressure of liquid is = to external pressure above liquid
Normal boiling point
Temperature at which the vapor pressure of a liquid equals 1 atm
The Clausius-Clapeyron Equation
ln P2/P1 = (-ΔHvap/R) (1/T2-T1)
R = 8.314 J/mol K
T = in Kelvin
Supercritical fluid
Properties are intermediate between a liquid and gas
Occurs at critical temperature and pressure
Sublimation
Phase transition solid to gas - endothermic
Deposition
Phase transition from gas to solid - exothermic
Fusion
AKA melting
Phase transition from solid to liquid - endothermic
Freezing
Phase transition from liquid to solid - exothermic
Heat (enthalpy) of fusion
ΔHfus = -ΔHcrystallization
Somewhat temperature dependent
The amount of heat energy required to melt one mole of a solid (kJ/mol)
Uniqueness of water
Liquid at room temperature (despite low molar mass)
Excellent solvent for polar & ionic compounds
Very high specific heat capacity
Expands when it freezes (unusual)
(Solid less dense than liquid – also unusual)
(Because of strong hydrogen bonds)
Equation for heat involved in completion of a phase change
q = nΔHtransition
heat = # of mols * heat of [transition]
Equation for heat involved in temperature change
q = (m) (Cs) (ΔT)