Liquids

Intermolecular Forces of Attraction

the strength this is the fundamental difference between states of matter

gas - liquid - solids

increasing imfa

Intermolecular Forces

forces that occur between molecules

Types of Intermolecular Forces (Weakest to Strongest Forces)

1. London Dispersion Forces

2. Dipole-Dipole Forces

3. Hydrogen Bonding

4. Ion-Dipole Forces

Van Der Waals Forces

other term for ldf and dipole-dipole forces

London Dispersion Forces

exist among noble gas atoms and nonpolar molecules

Polarizability

tendency of an electron cloud to distort

Factors that Affect Dispersion Force in a Molecule

1. number of electrons in an atom

2. size of atom or molecule/molecular weight

3. shape of molecules with similar masses

Dipole-Dipole Forces

exhibited by molecules with polar bonds that behave in an electric field

Characteristics of Dipole-Dipole Forces

• only 1% as strong as covalent or ionic bonds

• forces grow weaker as distance between dipoles increases

Hydrocrabon

• usually nonpolar

• no O or N

ether

C-O-C

aldehyde

O=C-H

nitrile

C≡N

carboxillic

-C-OH

CO2H

very polar

(carboxillic)

increasing polarity means

increasing strength of dipole-dipole forces

Hydrogen Bonding

strong dipole-dipole forces can be noticed when H is bound to lo e pairs on highly electronegativite atoms like N,O, and F

Strength of Hydrogen Bonding Interactions can be characterized by:

• Polarity of the Bond

• Close Approach of the dipoles

• Small size of Hydrogen Atom

Ion-Dipole Interactions

• are found in solutions of ions

• the strength of these forces is what makes it possible for ionic substances to dissolve in polar solvents

Liquids

exhibit low compressibility, lack of rigidity, and high density

Surface Tension

is the resistance of a liquid to an increase in its surface area

Liquids with Large Intermolecular Forces

• tend to have high surface tensions

• tend to be highly viscous

• have relatively low vapor pressure

Capillary Action

is a spontaneous rising of a liquid in a narrow tube

Adhesive Forces

attract the liquid to the wall of the tube

Cohesive Forces

attract the liquid to itself

Viscosity

refers to the measure of a liquid's resistance to flow

low to high viscosity

haxane - heptane - octane - nonane - decane

Phase Change

conversion from one state of matter to another

heat of fusion

• the energy required to change a solid at its melting point to a liquid

• melting/freezing

heat of vaporization

• energy required to change a liquid at its boiling point to a gas

• vaporizing/condensing

heat of sublimation

• is the energy required to change a solid directly to a gas

• subliming/depositing

Endorhermic Process

Solid to Liquid to Gas

Exothermic Process

Gas to Liquid to Solid

Heating Curves

a plot of temperature vs. heat added

Formula for Heat

Heat = m × Cp × 🔺️T

Heat = m × 🔺️Hvap

Phase Change

in a heating curve, when the temperature is constant it indicates that there is a

Increase of Temperature

in a heating curve, an upward line indicates that there is an

Dynamic Equilibrium

liquid molecules evaporate, and vapir molecules condense at the same rate

Vapor Pressure

• is present only in equilibrium

• also called equilibrium vapor pressure

Boiling Point

is the temperature at which vapor pressure equalts atmospheric pressure

Normal Boiling Point

is the tempeat which its vapor pressure is 760 torr or 1 atm

Normal Melting Point

temperature at which solid and liquid states have identical vapor pressure, and toal vapor pressure = 1 atm

Clausius-Clapeyron Equation

the natural log of the vapor pressure of a liquid is inversely proportional to its temperature

ln(Pvap) = - 🔺️Hvap/R (1/T) + C

Clausius-Clapeyron Equation

ln(Pvap, T1/Pvap, T2) = 🔺️Hvap/R (1/T2 - 1/T1)

when the values of Hvao and Pvap at constant temperature are known

Phase Diagrams

a convenient way of representing the phases of a substance as a function of its temperature and pressure

Triple Point

the temperature at which all three phases exist simultaneously

Critical Point

the critical pressure and critical temperature, together, define thus point

Critical Temperature

the temperature above which a liquid cannot be liquefied, irrespective of pressure applied

Critical Pressure

Pressure required to produce liquefaction at critical temperature