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chem2 chp11


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What are some characteristics of a gas?
-assumes both volume and shape of container
-is compressible
-flows readily
-diffusion within a gas occurs rapidly
What are some characteristics of a liquid?
-assumes shape of the portion of the container it occupies
-does not expand to fill container
-is virtually incopressible
-flows readily
-diffusion with a liquid occurs slowly
What are some characteristics of a solid?
-retains its own shape and volume
-is virtually incompressible
-diffusion in a solid occurs very slowly
What does the state of a substance depend on?
it depends largely on the balance between the kinetic energies of the particles and the interparticle energies of attraction
What are the types of intermolecular forces?
ion-dipole forces, dipole-dipole forces, London dispersion forces, and hydrogen bonding
Describe ion-dipole forces.
they exist bwetween and ions and the partial charge on the end of a polar moecule.
Describe dipole-dipole forces.
-are effective only when polar molecules are very close together and are generally weaker than ion-dipole forces.
Describe London dispersion forces.
the temporary dipole on one atom can induce a similar temporary dipole on an adjacent atom, causing the atoms to be attracted to each other, this interaction is call the London dispersion force.
What is polarizablity?
The ease with which the electron distribution in a molecule is distorted.
Dispersion forces increase in strenght with what?
increasing molecular weights
Dispersion forces operate on which molecules?
all molecules
Of Br.2, Ne, HCl, HBr and N.2, which is likely to have (a) the largest intermolecular dispersion forces, (b) the largest dipole-dipole attractive forces?
(a) Br.2 ( largest molecular weight), (b) HCl (largest polarity)
Describe Hydrogen bonding.
is a special type of intermolecular attraction between the hydrogen atom in a polar bond (particularly an H-F, H-O, H-N bond) and an unshared electron pair on a nearby small electronegative ion or atom( usually F,O,N atom in another molecule.
Which of the following substances is significant hydrogen bonding possible: methylene chloride (C.H2.Cl2), phosphine (P.H3), hydrogen peroxide (H.O.O.H) or acetone (C.H3.C.O.C.H3)
hydrogen peroxide, H.O.O.H
What is viscosity and describe it?
the resistance of a liquid to flow. The greater the viscosity the more slowly it flows. Viscosity decreases with temp.
What is surface tension and describe it?
is the energy required to increase the surface area of a liquid by a unit amount.
cohesive forces?
intermolecular forces that bind similar moleules to one another, ex. hydrogen bonding in water.
adhesive forces?
intermolecular forces taht binda a substance to a surface
used to describe the surface of a substance. ex. the water menisucus in a glass tube curves down where as the menisucus of mercury in a glass curves up.
capillary action?
the rise of liquids up very narrow tubes
fusion also called?
the melting process of solid to liquid
heat of fusion?
the enthalpy change, &H, for melting a solid
heat of vaporization?
the enthalpy change,&H, for vaporization of a liquid
heat of sublimation?
the enthalpy change, &H, for vaporization of a solid
heating curve?
a graph of the tmperature of the system versus the amount of heat added
supercooling / superheating?
sometimes as we reomve heat from a liquid, we can temporarily cool it below its freezing point, conversely heat it over its melting point.
critical temperature?
the highest temperature at which a distinct liquid phase can form
critical pressure?
the pressure required to bring about liquefaction at this critical temperature
What is vapor pressure?
the pressure exerted by a vapor in equilibrium with its liquid or solid phase
Describe dynamic equilibirium (or equilibrium).
the condition which two opposing processes are occurring simultaneously at equal rates.
What is volatitily?
tending to evaporate readily. ex. gasonline has high volaitity and motor oil has low volatiity.
What is the normal boiling point?
the boiling point of a liquid at 1 atm.
What is a phase diagram?
a graphical way to summarize the conditions under which equiliria can exist between the different states of matter.
What is the triple point?
the point on a phase diagram where all three states are in equilbrium
What are the two forms that solids can be?
crystalline and amorphous
Describe crystalline solid
-the atoms, ions, or molecules are ordered in well defined arrangements.
-usually have flat surfaces, or faces, that make definite angles with on another
-ex. diamond and quartz are crystalline solids
Describe amorphous solid
-a solid whose particles have no orderly structure.
-no well defined faces and shapes.
-many amorphos solids are mixtures of molecules that do not stack together.
-do not melt at a specific temperature but soften over a temperature range
-ex. rubber and glass
What is the unit cell?
the repaeating unit of a solid, the crystalline "brick,"
What is a crystal lattice?
an imaginary network of points on which the repeating unit of the structure of a solid (contents of the unit cell) may be imagined to be laid down so that the structure of the crystal is obtained. Each point represents and identical environment in the crystal.
Descrive the primitive cubic unit cell.
a cubic unit cell in which the latice points are at the corners only
Describe the body centered cubic cell.
a cubic unit cell in which the lattice points occur at the corners and at the center
Describe the face centered cubic cell.
a cubic unit cell that has lattice points at each corner as well as at the center of each face.
The element iron crystallizes in a form called a-iron, which has a body-centered cubic unit cell. How many iron atoms are in the units cell?
The body-centered cubic unit cell of a particular crystalline form of iron is 2.8664 A on each side. Calulate the density of the form of iron.
7.8753 g/cm3
Describe molecular solids
-they consist of of atoms or molecules held togther by intermolecular forces (dipole-dipole, london, and hydrogen bonding)
-becase of these forces they are usually soft and typically have low melting points
-poor thermal and electrical conductors
Describe covalent-network solids
-consist of atoms held together in large networks or chains by covalent bonds
-are physically harder and have higher boiling points because of the covalent bonds
-poor thermal and electrical conductors
-ex. diamond and graphite
Describe ionic solids
-consist of ions held together by ionic bonds
-strength of ionic bond depends on the charge of the atoms
-poor thermal and electrical conductors
Describe metallic solids
-consist of entirely metal atoms
-good conductors of electricity
-are usually face centered cubic or body centered cubic

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