Prince George’s Community College

CHM1010 (Shah)

Chapter 11ALiquids, Solids, and IMF


  • Solids, Liquids, and Gases
  • IMF: London Dispersion Forces, Dipole-Dipole Forces, Hydrogen bonding, Ion Dipole Forces
  • Define: Surface tension, Viscosity
  • Vaporization and Vapor Pressure
  • The Clausius-Clapeyron Equation: Vapor Pressure and Temperature
  • Sublimation, Fusion
  • Crystalline solids

States of matter: Solid, liquid, and gas

State / Density / Shape / Volume / Strength
of IMF / Compressible
Solid / High / Definite / Definite / Strong / Generally can’t be compressed
Liquid / High / Indefinite / Definite / Moderate / Not easily compressible
Gas / Low / Indefinite / Indefinite / Weak / Easily compressible
Crystalline solids / Amorphous solids
The atoms or molecules that compose them are arranged in well ordered three –dimensional array example: salt / The atoms or molecules that compose them have no long range order (different from the normal solid state). Example: glass

Intramolecular forces (covalent bond) are relatively strong bonding forces that hold atoms together in the molecular unit.

Intermolecular forces: Inter molecular forces are the relatively weak forces that hold one molecular unit to other molecular unit. IMF as a whole are usually called van der Waals forces.

Types of IMF:

Dipole -dipole forces

London dispersion forces

Hydrogen bonds: A hydrogen bond between molecules is an intermolecular force in which a hydrogen atom covalently bonded to

another atom (N, F, O)

Ion- dipole forces:

Dipole - Dipole forces:

Molecules with dipole moments can attract each other electro statically by lining up so that positive and negative ends are close to each other. This is called a dipole - dipole attraction. The forces created by this attraction are called Dipole - Dipole forces.

Dipole - Dipole forces are typically only about 1% as strong as covalent or ionic bonds. Particularly strong dipole - dipole forces, however, are seen among molecules in which Hydrogen is bound to a highly electronegative atom such as N, O or F (because of great polarity and close approach of the dipoles). This is also called a hydrogen bonding.

Dipole forces affect melting points and boiling points. Hydrogen bonds are stronger dipole forces.

More polar the molecules are, the stronger the dipole forces between molecules.

Hydrogen bond is much stronger in HF than HBr, HI, and HCl

EN difference is  1.8, 0.8, 0.5, 1.0

London Disperse forces: The forces that exist among noble gas atoms and nonpolar molecules are called London dispersion forces.

London Dispersion forces result from temporary dipoles.

The Importance of London dispersion forces increases greatly as the size of the atom increases (as the # of electrons in the molecules increases).

Note: London and dipole forces between molecules are usually much weaker than ionic forces in crystals. The very strong forces of ionic bonds lead to much higher melting points and boiling points for ionic compound than for molecular compounds.

Example: M.P. for NaCl is 801°C and for I2 is 114°C.

The magnitude of LDF depends on molar mass and the shape of the molecule.

For the same family: as molar mass increases strength increases so boiling point increases.

Among n-pentane, n-hexane, n-heptane: n-heptane has a higher BP.

For the same molar mass: shape determines the strength: n-pentane and neopentane: n-pentane has a higher BP. (larger the molecule, higher the BP is) Another example: Formaldehyde and ethane

For the same molar mass if H bond is present: The molecule with “H” bond has higher BP, and MP than molecule with no “H” bond.

Ethanol and Dimethyl ether

Ion-Dipole Force:

Ion-Dipole Force occurs when an ionic compound is mixed with a polar compound. It is especially important in aq. Solution of ionic compounds. Example: Sodium chloride is mixed with water.

Surface tension: The surface tension of a liquid is the energy required to increase the surface area by a unit amount.

Surface tension increases as IMF increases

Viscosity: The resistance of a liquid to flow. Stronger the IMF higher the viscosity is.

Capillary action: The ability of a liquid to flow against gravity up a narrow tube when taking a blood sample.

Vaporization and Vapor Pressure:

Conversion from liquid to gas is called vaporization. Opposite to vaporization (evaporation) is called condensation.

Volatile: Liquids that vaporize easily is known as volatile and those that don’t vaporize easily is called nonvolatile. The rate of vaporization increases with increasing temperature/surface area or decreasing strength of IMF.

Heat of vaporization: The amount of heat required to vaporize one mole of a liquid to gas is its heat of vaporization (∆Hvap.)

Heat of vaporization of water at its normal boiling point of 100°C is -40.7kJ/mol (this process is endothermic)

H2O(l)  H2O(g)∆Hvap. = +40.7kJ/mol

Heat of vaporization of 1mol of water condenses at its boiling point of 100°C is -40.7kJ/mol (this process is exothermic)

H2O(g)  H2O(l)∆Hvap. = - 40.7kJ/mol

Example: Calculate the mass of water in g that can be vaporized at its boiling point with 155kJ of heat. (answer: 68.6g H2O)

Calculate the amount of heat in kJ required to vaporize 2.58kg of water at its boiling point. (5830kJ)

Dynamic equilibrium: Dynamic equilibrium occurs when the rate of condensation is equal to the rate of evaporation.

Vapor pressure: The pressure of a gas in dynamic equilibrium with its liquid is called its vapor pressure. The vapor pressure of a particular liquid depends on the IMF present in the liquid and temperature.

Weak IMF result in volatile substances with high vapor pressures because IMF are easily overcome by thermal energy. Strong IMF result in nonvolatile substances with low vapor pressures.

Boiling point: The boiling point of liquid is the temperature at which its vapor pressure equals the external pressure.

The normal boiling point of a liquid is the temperature at which its vapor pressure equals 1 atm.

The Clausius – Clapeyron equation:

ln Pvap. = -(∆Hvap/R)(1/T)+ lnẞ

slope = - ∆Hvap/R

∆Hvap = -slope x Rwhere R = 8.314 J/mol.K

ln(P2/P1) = - (∆Hvap/R)(1/T2 - 1/T1)

  1. The vapor pressure of CH2Cl2 was measured as a function of temperature, and the following results were obtained.

Temperature (K) / Vapor Pressure (torr)
200 / 0.8
220 / 4.5
240 / 21
260 / 71
280 / 197
300 / 391

Determine the heat of vaporization of dichloromethane.


  1. Methanol (CH3OH) has a normal boiling point of 64.6°C and a heat of vaporization 35.2kJ/mol. What is the vapor pressure of methanol at 12.0°C? (answer: 73.4 torr) R = 8.314 J/mol.K

Sublimation: The process by which a substance goes directly from the solid to the gaseous state without passing through the liquid state. Example: Sublimation of NH4Cl, solid CO2 (dry iice)

Deposition: The opposition to sublimation is deposition, the

transition from directly gas to solid.

Fusion (melting): The increasing thermal energy causes the

water molecules to vibrate faster and faster. At the melting

point, the molecules have enough thermal energy to overcome

the IMF that hold them at their stationary points, and the solid turns into liquid. This process is known as fusion or melting.

The opposite of melting is known as freezing.

MeltingH2O(s)  H2O(l) ∆Hfus. = +6.02kJ/mol at mp (0°C)

Freezing H2O(l)  H2O(s) ∆H = -∆Hfus. = -6.02kJ/mol