QHEM Chapter 14: Liquids and Solids

Solids vs Liquids vs Gases

Solids=high density, slightly compressible, rigid (keeps its shape)

Liquid= Water molecules close together but can move around to some extent

Gas=low density, highly compressible, fill container

Density for ice vs water

Water=1.00g/ml

Ice=0.917 g/ml

Changes of state

Changes of state are physical changes so no chemical bonds are broken.

Phase Changes

When a substance changes from solid to liquid to gas, molecules remain intact. The changes in state are due to changes in the forces among molecules rather than in those within the molecule. This is bc it has to do with the speed and proximity of the water molecules.

Solid to liquid: As energy is added, motions of molecules increase and achieve a liquid’s greater movement and disorder characteristic.

Liquid to Gas: As more energy is added, the gaseous state is eventually reached with individual molecules far apart and interacting relatively little.

Intramolecular forces

WITHIN the molecule. Molecules are formed by sharing electrons between the atoms. Holds the atoms of a molecule together.

Intermolecular forces

forces that occur BETWEEN molecules (bonds between 2 molecules). Intermolecular bonds are weaker than intramolecular forces.

Possible phase changes

Gas—> liquid=condensation

Liquid—> gas =vaporization

Liquid—> solid =freezing

Solid—>liquid = melting (fusion)

Solid—> gas = sublimation

Gas—> solid = deposition

Phase changes have associated energy changes

Molar heat of fusion—enthalpy required to melt 1 mol of a solid substance

Molar heat of vaporization—Enthalpy required to change 1 mol of a liquid to its vapor.

Molar heat of sublimation—enthalpy required to change 1 mol of a solid to its vapor.

UNITS=kJ/mol of heat