GEN CHEM 1 | Phase Diagrams and Liquid and Solid Properties

Phase Diagrams

a visual representation that helps one understand what phase of matter a substance is under various temperatures, pressures, and other conditions

Solid Phase

region that is characterized by a fixed shape and volume; molecules have the greatest molecular order

Liquid Phase

region that is characterized by a fixed volume but indefinite shape

Gas Phase

region that is characterized by an indefinite volume and shape; molecules have the greatest randomness

Phase Boundaries

lines that separate the different phases, indicating the conditions one phase changes to another and showing that the 2 phases on either side of the line coexist in equilibrium

Triple Point

the unique set of conditions where all three phases coexist in equillibrium

Critical Point

end point of the liquid-gas boundary, beyond which these phases do not exist; the substance is a supercritical fluid, with properties of both liquids and gases

Melting/Freezing Curve

the curve that represents the transition between liquid and solid states; also shows the melting point

Vaporization/Condensation Curve

the curve that represents the transition between liquid and gas states; also known as the boiling point

Sublimation/Deposition Curve

the curve that represents the transition between solid and gas states

Phase Diagrams in Material Science

understanding the properties of materials and their transformations

Phase Diagrams in Chemistry

predicting reaction conditions and the stability of products

Phase Diagrams in Environmental Science

analyzing the behavior of substances in different environmental conditions

Phase Changes

happens when energy (usually heat) is added or removed from a substance, causing changes in molecular order

Energy Change and Molecular Order

The more heat is added to a substance, the more random the molecular order becomes.

Boiling Point of Water

373 K or 100 ºC at 1 atm

Melting Point of Water

273 K or 0 ºC at 1 atm

Sublimation Point of CO2

194 K or -78.5 ºC at 1 atm

Surface Tension

the amount of energy required to increase surface area of a liquid, the elastic tendency of a fluid surface which makes it acquire the least surface area possible

Surface Tension and Molecules

The molecules at the surface do not have other like molecules all around, so they cohere stronger with those directly associated with them on the surface. This means the stronger the intermolecular forces, the greater the surface tension.

Viscosity

It is the resistance to flow, which increases with the strength of the intermolecular forces since stronger forces make it more difficult for molecules to move with respect to one another

Factors Affecting Viscosity

Viscosity increases with molecular weight and decreases with higher temperature

Heat of Vaporization

amount of heat or energy necessary to vaporize 1 mole of a liquid, with the quantity kJ/mol

IMF and Heat of Vaporization

the Heat of Vaporization is determined by the strength of intermolecular forces that exist in the liquid; stronger intermolecular forces have a higher heat of vaporization

Crystalline Solids

particles are arranged in an orderly repeating pattern, leading to highly regular shapes, sharp melting points, and an ability to diffract x-rays; common examples are gemstones and minerals

Lattice

the symmetrical three-dimensional arrangement of atoms inside a crystal

Unit Cell

smallest repeating unit of a lattice

Amorphous Solids

particles are lack an orderly repeating pattern, leading to irregular shapes, a lack of sharp melting points, and a lack of ability to diffract x-rays; common examples are organic compounds; rubber, glass, and obsidian; can be made crystalline by slow cooling melt

Ionic Solids

• Composed of positive and negative ions connected by ionic bonding/electrostatic attraction among oppositely charged ions

• Hard, brittle, high melting points, poor conductor of electricity as a solid.

• Consists of all ionic compounds.

Metallic Solids

• composed of metal cations surrounded by a sea of electrons held together by metallic bonding or electrostatic attraction between metal ions and electrons

• malleable and ductile, good conductor of heat and electricity, has a wide range of hardness and melting points

• consists of metals and alloys

Molecular Solids

• composed of covalently bonded molecules held together by intermolecular forces

• has low to moderate melting points, soft, poor conductor of heat and electricity

• consists of usually amorphous solids

Network Solids

• consists of atoms held in an infinite 1,2, and 3-dimensional network held together by covalent bonding

• has wide range of hardness and melting points

• mostly poor conductor of electricity

• consists of gemstones and minerals (usually crystalline solids)