Chemistry 101 Final Unit 3

Question 1

What are gases’ physical properties?

Answer 1

• largely independent of their chemical composition
• highly compressible (Boyle’s law), thermally expandable (Charles’ law), low viscosity (resistance to deformation), low density, infinitely miscible (a mixture of gases)

Question 2

What is the ideal gas law formula?

Answer 2

PV: nRT
- P: pressure (atm) (1 atm: 760 torr: 760 mmHg)
- V: volume (L)
- T: absolute temperature (K)
- n: amount of gas (mol)
- R: gas constant (0.08206 atm/molxK)

Question 3

What are the 3 applications of the ideal gas equation?

Answer 3

1. molar mass determination
2. gas density
3. gas stoichiometry

Question 4

What is the kinetic molecular theory?

Answer 4

Model of ideal gas (explains behaviour of gas)
1. particles are in random motion
- collisions of particles with the walls are the cause for
pressure exerted by the gas
2. negligible particle volume
- volume of individual particles can be neglected (rounds to
0), as gas molecules are small compared to the distance
between them
3. particles collide with each other + container wall
4. particles collide with each other + experience no interparticle forces
- no attractive or repulsive forces between particles
5. constant total energy
- but energy is transferred in collisions with KE conserved

average KE of collection of gas particles: gas’ temperature

average KE of an ideal gas only depends on its temperature

Question 5

What are the 2 relationships between gases and temperatures?

Answer 5

1. different gas + same temperature
   
   • lighter gases: greater average speeds (look at atomic mass)
2. same gas, different temperature
   
   • higher temperature: greater average speeds (increase in KE:
     increase in average speed)

Question 6

What is the relationship between temperature, KE and motion?

Answer 6

Higher temperature: greater KE: greater motion
- note that lighter mole will have greater molecular speed

Question 7

What is ideal and non-ideal for gases?

Answer 7

• ideal: lower pressure, higher temperature
• non-ideal: higher pressure, lower temperature

Question 8

What occurs in real gases that violate the assumptions made in KMT?
1. no stickness: no interparticle forces
2. no size: no negligible particle volume

Answer 8

1. particles in a real gas experience weak interparticle attractions
   
   • interparticle attractions occur between separate atoms or
     molecules + are caused by imbalances electron distribution,
     these forces are important only over very short distances +
     are much weaker than bonding forces
2. particles in a real gas occupy a finite volume
   
   • at normal Pext, the space between particles is enormous
     compared with the volume of the particles themselves
   • increase Pext: decrease in free volume thus the volume of
     particles make up a significant portion of the container
     volume
   • at moderately high Pext, z values are lower than ideal
     values (2>1) due to interparticle attractions at very high
     Pext, values are greater than ideal (2>1) due to particle volume

Question 9

What is van der Waals equation used for?

Answer 9

Used to account for the non-ideal behaviour.

Question 10

What are phase changes?

Answer 10

When real gas’ behaviour deviates from being ideal when attractive forces between gas particles become significant, when these forces are strong enough: ex. gas becomes liquid.
- LDF: hold particles together, weaker than covalent bonds
- phase: a physically distinct homogeneous part of system

Question 11

What are intramolecular forces + intermolecular forces?

Answer 11

• intramolecular (bonding) forces
  
  • within a molecule, chemical behaviour of 3 states are all
    identical since they consist of the same molecule held
    together by the same covalent bonding forces
• intermolecular (antibonding) forces
  
  • between molecules, physical behaviour of the states differ
    since strength of forces differ

Question 12

What do phase changes depend on?

Answer 12

• intermolecular forces + KE of the moving particles
  
  • T increase: KE average increase (particles move faster +
    overcome attractions more easily)
  • T decrease: KE average decrease (particles move slower +
    attractions can pull them together closer more easily)

Question 13

Substance’s stage changes can absorb or release energy, what are the 6 changes?

Answer 13

1. s - l - g: energy’s absorbed (△H° fus, △H° vap)
   
   • s-l: melting, l-g: vaporization, s-g: sublimation
2. g - l - s: energy’s released (-△H° fus, -△H° vap)
   
   • g-l: condensation, l-s: freezing, g-s: deposition

Question 14

Which one is greater, △H° fus, △H° vap?

Answer 14

△H° fus «< △H° vap in general for all substances
- less energy to overcome the IMFs enough for molecules to
move out of fixed positions (melt a solid) than to fully
separate them (vaporize a liquid)

Question 15

Why is H2O a special case for phase changes?

Answer 15

Both △H° fus + △H° vap are large: stronger IMFs are needed to be overcome + hydrogen bonding.

Question 16

What is the equilibrium process?

Answer 16

Eventually rate of vaporization equals rate of condensation: equilibrium’s established.
- molecular level: molecules enter + leave at equal rates

Question 17

What is vapour pressure?

Answer 17

The measure of the tendency of a substance to change into the gaseous/vapour state from the liquid state.

Question 18

What is temperature’s effect on vapour pressure?

Answer 18

• changes the fraction of molecules moving fast enough to escape liquid: fraction slow to be recaptured
• T increase: vp increase: T increase leads to more molecules having enough energy to leave the surface

Question 19

What does vapour pressure depend on?

Answer 19

• type of liquid + temperature
  
  • molecules with weaker IMF forces are held less tightly +
    vaporize more easily
  • molecules with stronger IMF forces are held more tightly +
    vaporize less easily

Question 20

What is the relationship between vapour pressure + boiling point?

Answer 20

Substances with vp increase: bp decrease, which leads to volatile (tendency of substance to evaporate at normal temperature).

Question 21

What is the boiling point?

Answer 21

• temperature at which the vapour pressure (inside bubbles) equals the external pressure (usually atmospheric pressure).
• normal bp: temperature where vp: 1 atm

Question 22

For solid-liquid equilibria…

Answer 22

1. T increase: particles vibrate more rapidly until some have enough KE to break free of their positions: melting begins
2. more liquid molecules, some collide with solid and become fixed in position again
   
   • phases remain in contact: dynamic equilibrium when
     melting rate: freezing rate - the T when this happens is mp
3. liquids + solids are nearly incompressible since pressure has small effect on the melting + freezing rates

Question 23

For solid-gas equilibria…

Answer 23

1. substance sublimes, not melts since intermolecular forces aren’t great enough to keep molecules close when they leave solid state
2. some solids do have high enough vp to sublime at ordinary conditions (ex. dry ice is non-polar: weak IMF)

Question 24

What are phase diagrams?

Answer 24

• depicts which phase is most stable (at different temperature + pressure conditions)
• regions: indicates which one phase is most stable
  
  • generally, solids are stable at low T + high P while gases are
    stable at high T + low P
• lines: indicates which two phases coexist in equilibrium
  
  • generally, s is denser than l: increase in converts, l to s
    (water’s the exception)
• critical point: where liquid-solid line terminates
  
  • above Pc + Tc, the vapour can’t be liquified: supercritical
    fluid
  • when a liquid is heated in a closed container, its density
    decrease and at the same time more of the liquid vaporizes
    so the density of the vapour increases
• at cp: the densities become equal + phase boundary
  disappears, KE average is too high that vapour can’t be
  condensed at any pressure
• triple point: when solid, liquid + gas can coexist in equilibrium

Question 25

What are intermolecular forces?

Answer 25

1. only influences physical (not chemical) properties of a substance 2. strengths are in: mp + bp, heats of fusion + vaporization, surface tension + viscocity, solubility 3. not all substances are molecular - no molecules in simple ionic solids, extended network solids 4. van der Waal forces - nonbonding forces, very weak compared to chemical bonding forces

Question 26

What are the different types of chemical forces?

Answer 26

1. bonding - ionic: cation - anion - ions are attracted to other ions with opposite charge - covalent: nuclei + shared e-pair - metallic: cations - delocalized electrons 2. non-bonding or van der Waals - ion-dipole: ion charge - dipole charge - dipole-dipole: dipole charges - molecules with permanent dipole moments experience dipole-dipole interactions - molecules will orient to maximine + & - attractions + minimize like-charge repulsion - H-bond: polar bond to H-dipole charge - special type of dipole-dipole between molecules that have H atom bonded to small, very EN atom (N, O or F) - ion-induced dipole: ion charge - polarizable e-cloud - dipole-induced dipole: dipole charge - polarizable e-cloud - london dispersion (induced dipole - induced dipole): polarizable e-clouds - caused by molecule's polarizability, which temporarily makes that point of molecule negatively charged with the rest of the molecule positively charged

Question 27

What is polarizability?

Answer 27

- how easy it is to cause distortion to the e-cloud to create a dipole moment - nonpolar molecule: the distortion induces a dipole moment polar molecule: the distortion induces an increase in the existing dipole moment - increase # of electrons + increase molecular size: increase polarizability (boys + girls example) - increase down the group: since atomic size increases + larger e-clouds easier easier to distort - decrease across a period: increase Zeff: moves the atoms smaller + holds electrons more tightly - cations are less polarizable (smaller, less electrons) while anions are more polarizable (bigger, more electrons)

Question 28

What are liquids?

Answer 28

- have definite volume but aren't confined to shape of container, properties depend on IMF's strengths

Question 29

What is surface tension?

Answer 29

- liquid's resistance to increase its surface tension, the energy required to crease the surface tension by a given amount - depends on IMF present - when considering the forces acting on a particle at the surface VS in the interior - interior molecule: attracted by others on all sides - surface molecule: attracted by others below + sides, so it experiences a net attraction downward

Question 30

How do you get a high surface tension?

Answer 30

Strong IMF: the stronger the IMF between particles, the more energy it takes to increase SA, so the greater the SA

Question 31

What is the relationship between surface tension and temperature?

Answer 31

SA decrease: T increase (at higher T, the liquid molecules have increased average KE with which to break attractions to molecules in the interior)

Question 32

What is capillarity and wetting?

Answer 32

- capillarity: rising of a liquid in a tube - wetting: spreading of a liquid across a surface

Question 33

Consider competition between cohesive forces (within the liquid) and adhesive forces (between liquid + surface)...

Answer 33

- cohesive > adhesive: retains shape - cohesive < adhesive: liquid spreads out

Question 34

Ex. water + mercury...-

Answer 34

- water wets glass: mensicus is concave (molecules of the liquid are attracted to those in the container) - adhesive forces (glass-H2O) are stronger than cohesive forces (H2O-H2O) bottom of meniscus is below the H2O- glass contact line - mercury doesn't wet glass: meniscus is convex (molecules of the liquid are attracted to each other) - cohesive forces (Hg-Hg) are stronger than adhesive forces (Hg-glass) top of mensicus is above the Hg-glass contact line

Question 35

What is viscocity?

Answer 35

Resistance of a liquid to flow, strong increase (ex. honey + motor line) implies strong IMF. Affected by molecular shape.

Question 36

What is the relationship between temperature and viscosity?

Answer 36

Increase T: decrease viscosity: faster moving particles overcome IMF more easily, thus resistance to flow decreases with temperature increases.

Question 37

What is solubility?

Answer 37

- ability to be dissolved - solution (homogeneous mixture), solute (minor component, is dissolved), solvent (major component, the one doing the dissolving) - attractive forces between same molecules, ions (in solid) are replaced by similar attractive forces with solvent molecules (ex. solute-solvent forces)

Question 38

What are solids?

Answer 38

- have definite shape + volume (particles are tightly packed + barely move) - can be amorphous (poorly defined shapes due to their particles lack orderly arrangement) or crystallin solids (well defined shapes due to their particles occurring in an orderly arrangement)

Question 39

How do we describe the structure of crystals?

Answer 39

- by specifying a pattern + the atoms that belong to the pattern - highly symmetrical external form of crystals suggest regular ordered arrangement of atoms, we describe the contents of the unit cell, which then translated, reproduces entire crystal structure - lattice: ordered array of points that describe particles' arrangement that form a crystal - lattice is imaginary, the crystal structure is what's real

Question 40

What are the 3 different types of cubics?

Answer 40

1. simple cubic: 8 identical particles define the corners 2. body-centered cubic: 8 identical particles define the corners, 1 at the center 3. face-centered cubic: 8 identical particles define the corners, 6 at the center of each face

Question 41

What is coordination number?

Answer 41

The number of nearest neighbours of a particle in a crystal.

Question 42

How are different parts of a cube shared?

Answer 42

1. corner is shared by 8 cells: 1/8 contribution 2. face is shared by 2 cells: 1/2 contribution 3. edge is shared by 4 cells: 1/4 contribution 4. particles inside a cell are not shared: one whole atom or particle

Question 43

What are the 2 different packings?

Answer 43

1. hexagonal closet packing - coordination number: 12 - 6 atoms per unit cell 2. cubic closest packing - coordination number: 2 - 4 atoms per unit cell

Question 44

What are the 3 common types of structures found for metallic elements?

Answer 44

1. hcp - stacking sequence: AB AB... - lattice: primitive hexagonal 2. fcc - stacking sequence: ABC ABC - lattice: face-centered cubic 3. bcc - stacking sequence: (not closest-packed) - lattice: body-centered cubic

Question 45

What do combinations of 2 or more metals give?

Answer 45

Improved physical properties (strength, hardness, resistance to corrosion).

Question 46

What are the 3 ionic solids?

Answer 46

1. sodium chloride structure (rock salt) - face-centered cubic array of anions with an interpenetrating fcc cation lattice - the smaller Na+ ions end up in the holes between the larger Cl- ions; thus, each Na+ is surrounded by 6 Cl- & vice versa 2. zinc blende structure - zinc lattice is best thought as fcc arrangement of anions, occupying one half of the tetrahedral holes - each ion is 4-coordinate and not a tetrahedral geometry 3. fluorite structure - common among salts with a 1/2 cation/anion ratio that have relatively large cations + small anions - antifluorite structure is common in compounds with a 2/1 cation/anion ratio and a relatively large anion, the ion arrangement is the opposite of that in the fluorite structure

Question 47

Carbon occurs in several elemental forms (allotropes) diamond + graphite. What are the differences?

Answer 47

1. diamond - bonding: adopts fcc unit cell with each C tetrahedrally bound to 4 others in an endless array, electrons are localized - properties: transparent, poor thermal + electrical conductors - uses: jewelry, drilling 2. graphite - bonding: occurs as stacked flat sheets of hexagonal C rings with a strong sigma-bond framework + delocalized pi-bonds - properties: soft + slippery, good electrical conductivity - uses: pencils, lubricants, dry cell

Question 48

What are fullerenes?

Answer 48

Group of carbon allotropes based on large molecular clusters of carbon atoms; prototype is the C60 molecule.

Question 49

What are the 3 components of the ideal gas law?

Answer 49

1. Boyle's Law describes relationship between volume and pressure, states that volume is inversely proportional to temperature. 2. Charles' Law describes the relationship between temperature and volume, states that volume is directly proportional to temperature. 3. Avogadro's Law states that volume is directly proportional to amount.