CHEM 1212: Exam 1
90 Cards in this Set
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The forces holding solids and liquids together
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intermolecular forces
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intermolecular forces are a function of:
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1 - charge
2 - polarity
3 - molar mass
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What are the four important intermolecular forces and rank them from strongest to weakest
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1 - ion ion interactions
2 - hydrogen bonding
3 - dipole dipole
4 - Dispersion forces
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The force of attraction between two oppositely charged ions is governed by
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Coulomb's law
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In terms of intermolecular forces, greater charge = _____
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stronger attraction
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In terms of intermolecular forces, greater distance = ___
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weaker attraction
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Coulomb's law determines what two things?
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1 - the melting and boiling points of ionic compounds
2 - the solubility of ionic compounds
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dipole dipole interactions become less important as _____
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temperature increases
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dipole dipole compounds are more volatile than ionic compounds because _____
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they are held less tightly
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Strong H-bonding occurs among ______
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polar covalent molecules containting H bonded to either F, O, or N
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The molecule that has an H attached to either F, 0, or N
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hydrogen bond donor
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the molecule that has an F, O, or N
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hydrogen bond acceptor
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What forces are present between all types of molecules
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london dispersion forces
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Dispersion forces are stronger for molecules with ______
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more electrons or that are larger
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Dispersion forces are caused by ____
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the polarization of the e- cloud of an atom or molecule
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Polarizability increases with increasing ____
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number of e- and therefore with increasing sizes of molecules
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London dispersion forces are a function of ______
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molecular polarizibility
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5 properties of a liquid
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particles are in constant motion
- particles are in close contact
- liquids are almost incompressible
- liquids do not fill the container
- intermolecular forces are relevant
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process in which a substance in the liquid state becomes a gas
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Vaporization or condensation
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Vaporization is dependent on _____
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temperature
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describe the idea of "cooling by evaporation"
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only the higher energy molecules can evaporate from the liquid. so then the liquid cools because the high energy hot ones have left
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When molecules of liquid are in the vapor state, they exert a ______
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vapor pressure
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____ is the pressure exerted by a vapor over a liquid in a closed container
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equilibrium vapor pressure
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At equilibrium, rate of evaporation = _____
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rate of condensation
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The vapor pressure of a liquid is seen to _____ with temperature
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increase exponentially
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The rate of evaporation equals the rate of condensation in a closed container
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dynamic equilibrium
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The vapor pressure of a liquid is a measure of the _______
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tendency of its molecules to escape from the liquid phase and enter the vapor phase at given T
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Vapor pressure of liquids always increase as _____
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temp increases
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liquids that are easily vaporized and have relatively high vapor pressures
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volatile liquids
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What do stronger attractive forces do for vapor pressure?
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lower it
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As long as some liquid remains in contact with the vapor, the vapor pressure does not depend on ____
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volume or surface area
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Three things the Clausius-Clapeyron equation is used for
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- predict the vapor P of liquid at new T
- determine what T we must heat something to get specific vapor P
- calculate delta H if we know
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What is the Clausius-Clapeyron Equation?
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ln (P2/P1) ≈ (ΔHvap / 8.314 J mol-1 K-1) (1/T1 - 1/T2)
The equation relates the vapor pressure of a substance at 2 different temperatures as a function of its enthalpy of vaporization.
It can also relate the vapor pressures over a solid in terms of the enthalpy of sublimation.
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Temperature at which a liquids vapor pressure is equal to the external pressure
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boiling point
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What is the critical point?
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point at which a high enough temp and pressure has been reached so that the interface between liquid and gas disappears
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Temperature above which a gas cannot be liquefied
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critical temp
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the pressure required to liquefy a gas at its critical temp
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critical pressure
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the combination of critical T and critical P
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critical point
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A substance at a temperature above its critical temperature
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supercritical fluid
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a measure of the unequal attractions that occur at the surface of a liquid or a measure of inward forces that must be overcome to expand the surface area of a liquid
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surface tension
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the ability of a liquid to rise or fall in a glass tube or other container
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capillary action
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forces that hold liquids together
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cohesive forces
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forces between a liquid and a solid surface
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adhesive forces
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the resistance to flow in a liquid
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viscosity
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Viscosity ___ with increasing T
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decreases
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noncrystalline solids, have no well-defined, ordered structure
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amorphous solids
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have well defined structure and sharp melting temperatures
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crystalline solids
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4 properties of solids
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1 - molecules, atoms, or ions locked into crystal lattice
2 - particles are close together
3 - exhibit strong intermolecular forces
4 - highly ordered, rigid, incompressible
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the smallest repeating internal unit that has the symmetry characteristics of the solid
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unit cell
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2 reasons why unit cells are important
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1 - a number of metals, ionic solids, and intermetallic compounds crystallize in cubic unit cells
2 - it's relatively easy to do calculations with these unit cells
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3 variations of the cubic crystal system
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- Simple or primitive
- body centered
- face centered
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how many particles are in each of the three unit cells?
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Simple - 1
BCC - 2
FCC - 4
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Radius equation for simple cubic
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r = a/2
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radius equation for body centered
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r = [(a)sqrt(3)]/4
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radius equation for face centered
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r = [(a)sqrt(2)]/4
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have ions that occupy the positions in the unit cell
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ionic solids
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____ was introduced to rationalize covalent bonding in molecules and can also be used to describe metallic bonding
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molecular orbital theory
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Idea that the electrons are associated with all the atoms in the crystal and not with specific bonded atoms
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delocalized
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a barrier to the promotion of electrons to a higher energy level
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Band gap
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naturally occurring property of the pure metal
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intrinsic semiconductors
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conductivity of material is changed by adding/doping the material with a different element
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extrinsic semiconductors
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Why do ionic compounds have high melting points?
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because ion ion interactions are so strong
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The lattice energy of a salt is dependent upon _____
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charge and size of the ions
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The energy released when a mole of formula units of a solid is formed from its constituent ions in the gas phase
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crystal lattice energy
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The crystal lattice energy is a measure of the ____
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attractive forces in a solid
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Crystal lattice energy increase as the _____
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charge density increases
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Charge density = ____
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ionic charge / ionic radius in angstrums
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four different ways to categorize solids
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- molecular
- network covalent
- ionic
- metallic
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characterized by relatively strong intramolecular bonds between the atoms that form the molecules
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molecular solids
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solid in which conventional chemical bonds hold the subunits together
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network solids
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salts that are held together by the strong force of attraction between ions of opposite charge
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ionic solids
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force of attraction in ionic solids depends on ____
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square of the distance between the positive and negative charges
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solids that do not have a regular structure
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amorphous solids
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temperature at which the lattice of a solid collapses into a liquid
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melting point
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energy required to melt a solid
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enthalpy of fusion
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conversion of a solid into a vapor
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sublimation
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used to show the relationship between phases of matter and the P and T
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phase diagrams
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indicates the condition at which all 3 phases coexist in equilibrium
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triple point
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homogenous mixture of two or more substances in a single phase
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solution
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component present in a larger amount in a solution is called the _____
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solvent
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Molarity
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Mols/liters of solution
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molality
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mols/kilo solvent
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Mole fraction
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(X) moles of component A divided by total moles
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Weight percent (% w/w)
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mass of one component divided by total mass of the mixture x 100
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the concentration of solute in equilibrium with undissolved solute in a saturated solution
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solubility
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A solution in which undissolved and dissolved particles are in equilibrium is
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saturated
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more solute can be dissolved in the solvent
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unsaturated
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higher than saturated concentration of solute
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supersaturated
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the ability of one liquid to dissolve into another
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miscibility
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when two liquids do not form a solution but exist in contact with each other such as oil and water
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Immiscible
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CHEM 1212: Exam 1