Phase diagrams, triple point, critical state of the substance Presentation

Types of Intermolecular Forces
Properties of liquids and solids
Phase change diagrams
Heating/cooling curve
Vapor pressure curve

Brainteaser!!!!

If substances at the same temperature have the same kinetic energy, why are they all not liquids, solids, or gases?

Intermolecular Forces

Intermolecular Forces are attractive forces between molecules. Think interstate!
Intramolecular Forces are attractive forces that hold molecules together
Inter vs. Intra
41 kJ to vaporize 1 mole of H2O
930 kJ to break all O-H bonds in one H2O molecule

Phases of matter

Gases – molecules are widely separated and the “fluid” is compressible
Liquids – molecules are more tightly packed and liquids are relatively incompressible
Solids – molecules are tightly packed and solids are incompressible and rigid

Liquids

IMF’s limit the range of motion of particles in a liquid

Density – Liquids have a higher density at 25 °C than gases

Fluidity – Ability to flow

Viscosity – Measure of the resistance of a liquid to flow

Surface tension – The energy required to increase the surface area of a liquid by a given amount

Surface Tension

The energy required to increase the surface area of a liquid by a given amount

Molecules in the center of a liquid are exposed to IMF from all sides

Molecules on the surface of a liquid are not exposed to IMF from all sides

In order to increase the surface area of a liquid the molecules in the interior of the liquid must move to the surface and the IMF’s must be broken

Capillary Action

Water molecules “cling” to the surface of the graduated cylinder by adhesion

Adhesion is the force of attraction between different types of molecules

Cohesion is the force of attraction between the same type of molecules

What force must be strongest for water to cling to the glass tube?

If adhesion forces are stronger than cohesion forces water will be drawn up the sides of the cylinder

Solids

Tightly packed molecules that are rigid and cannot be compressed
Density is highest in solids (except in water!!!)
Crystalline solid – solid whose atoms, ions, or molecules are arranged in an orderly, geometric, 3-D structure
Amorphous – atoms are randomly arranged because they typically cool too quickly. No order exists in the solid.

Types of Solids

Crystalline – a well defined arrangement of atoms; this arrangement is often seen on a macroscopic level. (p.402)
Atomic solids
Ionic solids
Molecular solid
Covalent network
Metallic
Units points that can be repeated in three dimensions to form a lattice

Phase Changes

Melting – the change from a solid to a liquid
Melting Point – T at which forces holding lattice together are broken
Vaporization- the change from a liquid to a gas
Sublimation – the change from a solid to a gas
Condensation – the change from a gas to a liquid
Deposition – the change from a gas to a solid
Freezing – the change from a liquid to a solid

GAS

SOLID

LIQUID

CONDENSATION

VAPORIZATION

SUBLIMATION

DEPOSITION

Phase Change Diagrams

Relationship between T and P
Triple point – P and T at which substance can coexists as a gas, liquid, and solid
Critical point – T at which a substance can no longer remain a liquid regardless of the pressure

Phase Diagram for H2O

What is the difference between this diagram and the first?
The liquid solid line leans backwards!

Vapor Pressure

In a sealed container some water (l) changes phase to become water vapor and exerts a pressure over the surface of the liquid (if the container were open it would be considered partial pressure)

Heating Cooling Curve

Heating and cooling curve for H2O

Real Gas Isotherm

Critical state of the Substance

In thermodynamics, a critical point (or critical state) is the end point of a phase equilibrium curve. The most prominent example is the liquid-vapor critical point, the end point of the pressure-temperature curve that designates conditions under which a liquid and its vapor can coexist.

Critical state of the Substance

In thermodynamics, a critical point (or critical state) is the end point of a phase equilibrium curve. The most prominent example is the liquid-vapor critical point, the end point of the pressure-temperature curve that designates conditions under which a liquid and its vapor can coexist.

Critical parameters

Water: Тcr=401.2°С, Рcr=22.1 МPа

Nitrogen: Тcr=-146°С, Рcr=3.9 МPа