Chemistry CH. 13
Le Chatelier's principle
If a system at equilibrium is subjected to a stress, the equilibrium will be displaced in such direction as to relieve the stress.
Intermolecular forces
Forces that exist between molecules
Intramolecular forces
Forces that exist within a molecule; aka bonds.
Closest packing
(=Closed packed) - most efficient arrangement for spheres. 1. Hexagonal close-packed structure - 12 immediate neighbors -ABA layer arrangement (other page) 2. Cubic closed-packed structure (=face-centered unit cell) - 12 immediate neighbors -ABC layer arrangement (other page)
Desiccant
(=Dehydrating agent) substance that has high attraction for water and is used to remove moisture from a gas.
Examples of hydrated crystals:
* copper sulfate pentahydrate (CuSO4•5H2O) *Epsom salt (MgSO4•7H2O) * tin(II) chloride dihydrate (SnCl2•2H2O) * sodium tetraborate decahydrate (Na2B4O7•10H2O) * zinc chloride dihydrate (ZnCl2•2H2O)
Hydrogen bonds must have:
-both bonds must have Nitrogen, Oxygen, Fluorine -Only one needs hydrogen - Hydrogen must be bonded to Nitrogen, Oxygen, or Fluorine
Hydrogen bond
A special (stronger) dipole-dipole interaction between the hydrogen atom bonded to an atom of a very high electronegative element and another atom (or ion) of one of the three electronegative elements. (other page)
Plasma
A state of matter made from a gas that has lost its electrons from heat --> where is plasma found 1. blood 2. neon signs 3. stars & lightning
Liquid crystal
A substance that exhibits one or more partially ordered liquid phases above the melting point of the solid form.
Critical temperature
A temperature above which a gas will no liquefy regardless of pressure.
Anhydrous
Expresses a chemical compound lacking water--> particularly to salts lacking their water of crystalline.
-What is the difference between extensive properties and intensive properties?
Extensive properties depends on the amount present; Intensive does not depend on the amount present + For crystals of the same substance, the intensive properties ARE the same. + For crystals of the same substance, the extensive ARE NOT the same.
Equilibrium
A balanced condition within a system of chemical reactions; substance form and break down at the same rate, and the number of molecules of each substance becomes definite and constant.
* A change in state
A change in state always involves a change in energy.
Network crystal
A chemical compound in which the atoms are bonded by covalent bonds in a continuous network.
Dynamic Equilibrium
A chemical equilibrium between a forward reaction and the reverse reaction where the rate of the reaction is equal.
Phase change
A conversion of a substance from one phase to another
Gas
A form of matter that takes the shape and volume of its container; a gas has no definite shape or volume.
Viscosity
A measure of a liquid's resistance to flow.
*All gases can be liquefied...
All gases can be liquefied --> requires a combination of lower temperature, and increase pressure. 1. critical temperature - a temperature above which a gas will no liquefy regardless of pressure. 2. critical pressure - minimum pressure required to liquefy a gas when it is at its critical temperature.
*All true solid substances are...
All true solid substances are crystalline.
Surface Tension
An inward force that tends to minimize the surface area if a liquid; it causes the surface to behave as if it were a thin skin.
Reversible Change
Change that can occur in opposite direction.
Metastable
Chemically unstable in the absence of certain conditions that would induce stability.
Liquefaction
Condensation of substances that are normally gases.
Volatile
Describe a substance that boils at a low temperature, evaporates rapidly at room temperature, and has a high vapor pressure.
Vapor
Describes the gaseous state of a substance that is generally a liquid or solid at room temperature.
Polar
Description of a covalent bond that has an unequal distribution of charge due to an unequal sharing of bonding electrons. (other page)
*Dispersion forces...
Dispersion forces exist among species of any type polar or nonpolar.
Face-centered cubic unit cell
Each particle has 12 immediate neighbors. (other page)
Cubic unit cell
Each particle has 6 immediate neighbors. (other page)
Bod-centered cubic unit cell
Each particle has 8 immediate neighbors. (other page)
*Each product has a reverse...
Each product has a reverse... 1. The reverse of melting is freezing. 2. The reverse of boiling (or evaporation) is condensing. 3. The reverse of sublimation is depositing. {ex. frost]
*Evaporation occurs only at the surface...
Evaporation occurs only at the surface of the liquid, but boiling takes place throughout the body of a liquid. Evaporation occurs at any temperature, but boiling takes place only at the boiling point.
Effervescent
Giving off bubbles.
*Greater molar mass and greater polarity....
Greater molar mass and greater polarity, tends to make substances form a condensed state, liquid, or solid.
Hygroscopic
Having a tendency to capture water molecule from the air; normally absorption
Enthalpy of vaporization
Heat required to boil one gram of a substance at its boiling point.
Enthalpy of fusion
Heat required to melt one gram of a substance at its melting point.
-Do network crystals have very high or very low melting points? Why?
High melting point because it has to break covalent bonds.
Hydrogen bonding in H2O accounts....
Hydrogen Bonding in H2O accounts for its density. 1. H-bonding in ice makes a wide-open crystal lattice. 2. When the ice melts the H-bonds break allowing molecular crowding. 3. Above 3.98 degrees Celsius (most dense) water expands with increased temperature.
*In a closed container...
In a closed container, the vapor phase is in dynamic equilibrium with its solid or liquid phase.
*In a dynamic equilibrium...
In a dynamic equilibrium, molecules escape and return to the solid or liquid surface continuously and at the same rate. (other page)
*Intramolecular forces are...
Intramolecular forces are considerably stronger than intermolecular forces. (example: red-rover game)
*Matter exists in...
Matter exists in three physical states under normal conditions.
Critical pressure
Minimum pressure required to liquefy a gas when it is at its critical temperature.
*Molecules have enough kinetic energy...
Molecules have enough kinetic energy to overcome the attractive force of neighboring molecules escape from the surface to form a vapor.
*Phase diagrams graphically represent...
Phase diagrams graphically represent changes of state at varying temperatures and pressures.
Triple point
Point at which the vapor, liquid, and solid states of a substance are an equilibrium.
Equilibrium vapor pressure
Pressure exerted by a vapor in equilibrium with its liquid --> depends on temperature and the nature of the liquid (intermolecular forces) - ↑ temp. --> ↑ e.v.p. - ↓ temp. --> ↓ e.v.p. - strong intermolecular --> low e.v.p. [ex. water] - weak intermolecular --> high E.v.p. [ex. polish remover]
Crystal
Rigid body in which the particles are arranged in a regular repeating pattern--> pattern determined by bonding.
Unit Cell
Simplest repeating unit in a crystal
*Substances that differ from predicted behavior...
Substances that differ from predicted behavior for melting and boiling points have two things in common: 1. molecules contain hydrogen 2. hydrogen is covalently bonded to a highly electronegative element --> Nitrogen, Oxygen, Fluorine
Normal boiling point
Temperature at which the vapor pressure of a liquid is equal to standard atmospheric pressure.
*Temperature remains constant...
Temperature remains constant during melting and boiling because the heat energy helps molecules overcome attractive forces (break intermolecular forces) and does not increase their average kinetic energy.
Deliquescent
Tending to absorb water from the surrounding atmosphere at ordinary temperature and pressure.
Sublimation
The Process in which a solid changes to a gas or vapor without passing through the liquid state.
*The Vander Waals forces...
The Vander Waals forces are affective only over short distances.
Capillary rise
The ability of a liquid to flow in narrow spaces without the assistance of external forces.
* The average kinetic energy of atoms or molecules...
The average kinetic energy of atoms or molecules in a substance is constant at a given temperature --> a few molecules have the average kinetic energy; most have a kinetic energy close to the average; a few have kinetic energy that are very large or very small.
*The hydrogen bond is weaker than...
The hydrogen bond is weaker than an actual chemical bond (is a dipole-dipole attraction-->intermolecular), but stronger than other dipole-dipole forces.
*The physical properties of liquids...
The physical properties of liquids are determined mainly by the nature and strength of the intermolecular forces present between their molecules.
*The physical state of a substance...
The physical state of a substance at room temperature depends on the molar mass and the intermolecular forces. 1. Ionic compounds- solids at room temperature (NaCl) 2. Polar Compounds with high molar mass- tends to be solids or liquids (high melting point) at room temperature. 3. Polar Compounds with low molar mass- tends to be liquids or gases (high boiling point) at room temperature. 4. Nonpolar molecule with low molar mass- tends to be liquid or gases (high boiling point) at room temperature. 5. Nonpolar molecule with low molar mass- gases at room temperature.
Condensed State
The solid and liquid states; phases in which particle interact strongly.
*The space lattice...
The space lattice and unit cell are mental models --> neither can be isolated from a crystal.
Melting point
The temperature at which a substance changes from a solid to a liquid; (also the freezing point)
Boiling point
The temperature at which the vapor pressure of a liquid is just equal to the external pressure on the liquid.
Space Lattice
Three dimensional arrangement of unit cells repeated over and over in a definite geometric arrangement.
Efflorescent
To lose water of hydration because the hydrate has a vapor pressure higher than water vapor in air.
Evaporation
Vaporization that occurs at the surface of a liquid that is not boiling.
Hydrated crystal
Water molecules trapped inside the crystal structure of some other compound, typically on ionic compounds.
*We will assume molar mass...
We will assume molar mass high if it is > or = 150g/mol.
Van der Waals forces
Weak attractive force between the nucleus of an atom in one molecule and the electron cloud of another molecule --> intermolecular forces 1. Dipole-dipole forces : Force between two permanent polar molecules (other paper) 2. Dipole-induced dipole forces : force between a permanent polar molecule and a no-polar molecule that has become a induced dipole --> non-polar molecule whose electron cloud has become distorted by an approaching ion or dipole. (other page) 3. Dispersion force : (=London Force) force between two particles due to the attraction between instantaneous of their change centers resulting in temporary dipoles (other page)
Amorphous
Without a clearly, defined shape or form.
