Liquids, Solids and Intermolecular Forces

The forces that hold molecules together are called intermolecular forces. ion –ion (interactions) forces ion –dipole forcesexist between an ion and a polar molecule Intermolecular forces as a whole are usually called van der Waals forces Dipol –dipol forcesexist between polar molecules London dispersion forces exist between nonpolar molecules Hydrogen bondingexist in the molecules that have a hydrogen atom bonded to an electronegative atom having unshared pair of electron like nitrogen, oxygen and fluorine.

Intermolecular forces as a whole are usually called van der Waals forces Dipol –dipol forcesexist between polar molecules London dispersion forces exist between nonpolar molecules Hydrogen bondingexist in the molecules that have a hydrogen atom bonded to an electronegative atom having unshared pair of electron like nitrogen, oxygen and fluorine.

Question What types of molecular forces are present in H 2 CCl 4 SCO NH 3

-The stronger intermolecular forces, the higher the melting/boiling point of subtances -Dispersion (london) forces exist between all molecules -As molar mases increases dispersion forces becomes stronger and the boiling point of subtances increase

Question List the following subtances in order of increasing boiling points? BaCl 2 H 2 HF CO Ne

List the following subtances in order of increasing boiling points? CCl4 Cl2 HF ClNO N2

Compare the boiling points of ethanol and dimetileter (they both have the same simple formula C 2 H 6 O, M A =46,07) CH 3 CH 2 OH CH 3 OCH 3

Compare the boiling points of CH 3 OCH 3 (M A =46) and H 2 O (M A =18)

Some Properties of Liquids and solids

Solids are incompressible, do not flow. In a solid the structural particles (atoms, ions or molecules) are in direct contact and intermolecular forces hold them into a fixed volume and shape. Liquids are incompressible, flow readily. In a liquid atoms or molecules are close together and intermolecular forces are strong enough to hold them in a fixed volume but not a definite shape.

Phase changes. Melting solid  Liquid Freezing liquid  Solid Vaporization liquid  Gas Condensation gas  Liquid Sublimation solid  Gas Deposition gas  Solid

Phase diagrams

The Triple pointis a point on a phase diagram which all three phases (liquid, solid and vapor) are in equilibrium with each other The critical pointis a point at which the liquid and vapor become indistiguishable. The density of liquid decrease, the surface tension of the liquid approaches zero. The meniscus between the liquid and vapor disappears. The critical temperature The temperature at the critical point Tc. above Tc the liquid phase of a pure subtances can not exist. The critical pressure The pressure at the critical point Pc

Supercritical Fluids

Carbon dioxide

Iodine

Some Properties of Liquids Cohesive Forces Intermolecular forces between like molecules. Adhesive Forces Intermolecular forces between unlike molecules. Surface Tension The resistance of a liquid to spread out and increase its surface area. Energy or work required to increase the surface area of a liquid. Viscosity is an internal resistance to flow liquids with strong intermolecular attractions are generally more viscous than liquids with weak intermolecular attractions.

Surface Tension The resistance of a liquid to spread out and increase its surface area. Energy or work required to increase the surface area of a liquid.

liquid contains some molecules in the gaseous or vapor state, the partial pressure of these gaseous molecules in equilibrium with a liquid is called vapor pressure. The vapor pressure of a liquid always increases as temperature rises

Question: an organic compound has a vapor pressure 0f 91.0 mmHg at 40°C. Calculate its vapor pressure at 25 °C, taking the heat of vaporization to be 5.31 x 10 4 J.mol

Question: the vapor pressure of napyhalene (C10H8)at 25 °C is 0.300mmHg, How many napthalene will sublime into an evacutaed 500.0ml flask?