Mcat Genchem Ii (Rev Notes)

Front 1

What is the formula for determining equivalents?

Back 1

Weight of cmpd/Gram Equiv Wt

GEW: molar mass/n

where n = #H's or OH's per molecule of acid/base in rxn

Front 2

What does the law of constant composition state?

Back 2

Any sample of a cmpd will contain same elements in ID mass ratio.

Front 3

What sets ionic compounds apart from other compounds in terms of empricial and molecular formulas?

Back 3

Ionic cmopounds only have empirical formulas

Front 4

How would you determine the molecular/empirical formula if given percent composition?

Back 4

Assume 100g sample (total), use percent as g, find moles, and work from there.

Front 5

Give an example of a combination reaction.

Back 5

A + B -> C

Front 6

Give an example of a decomposition reaction.

Back 6

A --> B + C

Front 7

Give an example of a single displacement reaction.

Back 7

A + BC--> B +AC

Front 8

Give an example of a double displacement reaction.

Back 8

AB + CD --> AD + CB

One of products removed from solution as ppt or gas!

Front 9

What is another term for double displacement reactions?

Back 9

Metathesis

Front 10

What category of reaction do neutralization reactions fall under?

Back 10

Double-displacement

Front 11

What is a general rule of thumb for balancing equations?

Back 11

Focus on least rep'd elements first, then work way to most rep'd of rxn

Front 12

If given 58.67g CO2, 27g H2O for:

CxHy + O2 (excess) --> CO2 + H2O

Solve for x and y

Back 12

58.67g CO2: 1.3mol CO2
27g H2O: 1.5 mol H2, thus 3 mol H

C1.3H3 x 3 = C4H9

Front 13

If given 1.5 kg of 5.2% NF3 sample. How many g NF3?

Back 13

1.5E3 x .052 = 75g NF3

Front 14

For:

aA + bB --> cC + dD

Describe the rate of the reaction in terms of concentrations of each product and reactant.

Back 14

rate = -1/a*delta[A]/deltat=-1/b*delta[B]/deltat=1/c*delta[C]/deltat=1/d*delta[D]/deltat

Front 15

For:

aA + bB --> cC + dD

What is the rate law?

Back 15

rate = k*[A]^x*[B]^y

Front 16

How are k, x, y determined for the rate law?

Back 16

Experimentally

Front 17

How can units of the overall reaction order be determined from units of k?

Back 17

If k is in units of M^-2s^-1, then reaction must be third order because k*M^3=Ms^-1

Units of rate are Ms^-1

Front 18

What is the general rate equation for zero order reactions? What are the units of k?

Back 18

rate = k
Units: s^-1

Front 19

What is the general rate equation for first order reactions? What are the units of k?

Back 19

rate = k
s^-1

Front 20

What is the general rate equation for second order reactions? What are the units of k?

Back 20

rate = k[A]^2 or
k[A][B]
or
k[B]^

M^-1s^-1

Front 21

What is the general rate equation for mixed order reactions?

Back 21

rate = k[A]^fraction

Front 22

What does the collision theory of chemical kinetics state?

Back 22

The rate of rxn is proportional to the number of effective collisions/second between reactin molecules

Front 23

Define effective collision.

Back 23

A collision that occurs only if molecs collide with correct orientation and sufficient force to break old bonds and form new ones

Front 24

What is the equation for the rate of a reaction in terms of effective collisions?

Back 24

r=fZ
f = fraction of effective collisions
Z = total number of collisions/second

Front 25

How does deltaH differ between endothermic and exothermic reactions?

Back 25

negative for exothermic
positive for endothermic

Front 26

What is the difference between a homogenous and heterogeneous catalyst?

Back 26

Homo: catalyst in same phase as reactants
Hetero: catlyst in distinc phase from catalyst

Front 27

For 2A<-->B+C
What is the rate law for the forward and reverse reactions?
What is Kc?

Back 27

rate(F)=k(f)[A]^2
rate(R)=k(r)[B][C]
rate(F)=rate(R)
thus
k(f)/k(r)=Kc=([B][C])/[A]^2

Front 28

For the following reaction:
aA + bB <--> cC + dD

What is Kc if the reaction occurs in three steps?

Back 28

Kc=(k1*k2*k3)/(k-1*k*-2*k-3)=[C]^c[D]^d/[A]^a[B]^b

AKA LAW OF MASS ACTION

Front 29

What does the reaction quotient measure? What does it equal at equilibrium?

Back 29

Degree to which rxn has gone to copmletion. Constant at equilibrium and equal to Kc.

Front 30

What class of reactants are NOT included in the rate constant equation?

Back 30

Pure solids/liquids

Front 31

Does Keq differ with temperature?

Back 31

Yes.

Front 32

Describe product/reactant concentrations if Keq>>1

Back 32

Shift to RIGHT, lots of products

Front 33

Describe product/reactant concentrations if Keq<<1

Back 33

Shift to LEFT, lots of reactants

Front 34

Describe product/reactant concentrations of Keq~1

Back 34

[R]=~[P]

Front 35

What does Le Chatelier's principle state in terms of species concentration, pressure and temperature?

Back 35

If you increase species, shift away. Decrease species, shift towards.

DeltaP inversely related to DeltaV; deltaP only affects gases (liquids/solids are incompressible)
Increase pressure-->Decrease volume-->shift reaction to side with fewer number of moles

Increase volume-->Decrease pressure-->shift to side with greater number of moles

If A<-->B + Heat
Decrease T-->go to right to replace lost heat
Increase T-->go to left to get rid of more heat
deltaT also affects Keq

Front 36

What does the law of mass action stay?

Back 36

Kf/Kr=Kc=[B][C]/[A]^2

Front 37

Do orders of reactions have to be whole integers?

Back 37

NO.

Front 38

How is Keq affected by the presence of a catalyst?

Back 38

It isn't.

Front 39

What is the equation for radioactive decay?

Back 39

[At]=[A0]*e^-kt

Front 40

What is the equation for half-life?

Back 40

t1/2=ln2/k=0.693*k

Front 41

What does it mean when a system is isolated? Provide an example of such a system.

Back 41

NO exchange of E or matter. Insulated bomb reactor.

Front 42

What does it mean when a system is closed? Provide an example of such a system.

Back 42

Exchange of energy but not matter. Steam radiator.

Front 43

What does it mean when a system is open? Provide an example of such a system.

Back 43

Can exchange both energy and matter. Pot of boiling water.

Front 44

What is the conversion factor for calories to joules?

Back 44

1 cal = 4.184 J

Front 45

Define heat capacity.

Back 45

mc

Front 46

What are standard conditions? How are they denoted?

Back 46

25ºC, 1 atm, standard state element (at room temp. ex: H2(g), H2O (l))

denoted by deltaHº, deltaSº, deltaGº

Front 47

Define heat of formation.

Back 47

deltaHºf=enthalpy change that occurs upon formn of 1 mole of compound from its elements in std state

Front 48

What is deltaHºrxn?

Back 48

deltaHºrxn=SumdeltaHºf products - SumdeltaHºf reactants

Front 49

What does Hess's law state?

Back 49

Enthalpies of reactions are additive and are state functions (path doesn't matter, only initial and final states).

Front 50

Define deltaHrxn in terms of enthalpy changes in bond formation/destruction.

Back 50

deltaHrxn=Energy in (bonds broken) - Energy out (bonds formed)

Front 51

deltaS=?

Back 51

qrev/T

Where qrev is q added to a system undergoing a reversible process and T is absolute temperature

Front 52

deltaSºrxn=?

Back 52

SumSºproducts-SumSºreactants

Front 53

deltaSuniverse=?

Back 53

deltaS system + deltaS surroundings

Front 54

At what point in a reaction is maximum entropy achieved?

Back 54

At equilibrium

Front 55

For reversible processes, what does deltaS universe=?

Back 55

0

Front 56

Defnie Gibbs free energy.

Back 56

The maximum energy released by a process available to perform useful work.

Front 57

deltaG=?

Back 57

deltaH-TdeltaS

Goose hunters take shotguns.
note TdeltaS = total q absorbed by system

Front 58

Describe the value of G at equilibrium.

Back 58

At a minimum

Front 59

deltaG=?

Back 59

deltaH-TdeltaS
Goose Hunters Take Shotguns

Front 60

Under what enthalpic and entropic conditions will a reaction always be spontaneous?

Back 60

Remember: T is always positive because it's in Kelvin

negative deltaH, positive deltaS

Front 61

Under what enthalpic and entropic conditions will a reaction always be non-spontaneous?

Back 61

T always positive because it's in Kelvin

Positive deltaH and negative deltaS

Front 62

Under what enthalpic and entropic conditions will a reaction be spontaneous at high temperatures?

Back 62

Remember T always positive because it's in Kelvin

Positive deltaH, positive deltaS

Front 63

Under what enthalpic and entropic conditions will a reaction spontaneous at low temperatures?

Back 63

Negative deltaH, negative deltaS

Front 64

Define deltaGºformation.

Back 64

deltaG when 1 mol of compound in standard state is formed from its elements in standard state under standard conditions

Front 65

deltaG=?

Back 65

deltaH-TdeltaS
Goose Hunters Take Shotguns

Front 66

Define deltaGº in terms of the equilibrium constant. Why is using Keq not a good idea? How can this be resolved?

Back 66

deltaGº=-RTln(Keq)

Once rxn starts, no longer in std conds, so use reaction quotient:
deltaG=deltaGº+RTln(Q)
where Q= ([C]^c[D]^d)/([A]^a[B]^b)
for aA + bB <-> cC + dD

Front 67

Under what enthalpic and entropic conditions will a reaction always be spontaneous?

Back 67

Remember: T is always positive because it's in Kelvin

negative deltaH, positive deltaS

Front 68

What will be the sign of deltaG for:
H2O(l) + heat --> H2O (g)

Back 68

Entropy will increase if T*deltaS>H, but is only true at T>100ºC (below this, deltaG is positive)

Front 69

Under what enthalpic and entropic conditions will a reaction always be non-spontaneous?

Back 69

T always positive because it's in Kelvin

Positive deltaH and negative deltaS

Front 70

What will be the sign of deltaG for:
2C6H6(l) + 15O2(g) --> 16CO2(g) + 6H2O(g) + Heat

Back 70

Heat is released so deltaH is negative
Increase in S (TdeltaS is positive)--2 gases have higher entropy than 1 gas and 1 liq

thus delta G is (-) and rxn is spont

Front 71

Under what enthalpic and entropic conditions will a reaction be spontaneous at high temperatures?

Back 71

Remember T always positive because it's in Kelvin

Positive deltaH, positive deltaS

Front 72

deltaHrxn = ?

Back 72

SumdeltaHprods-SumdeltaHreacts

Front 73

Under what enthalpic and entropic conditions will a reaction spontaneous at low temperatures?

Back 73

Negative deltaH, negative deltaS

Front 74

For:
N2(g)-->2N(g), deltaHºrxn=954.2kJ

What is deltaH of nitrogen?

Back 74

deltaHrxn=954.2=2*(deltaHN)-(deltaHN2)
deltaHN2=0 because N2 is in elemental state

thus 2deltaHN=945.2 then solve

Front 75

Define deltaGºformation.

Back 75

deltaG when 1 mol of compound in standard state is formed from its elements in standard state under standard conditions

Front 76

If deltaG is negative, can work be done?

Back 76

Yes, energy released can be coupled to less favorable reactions.

Front 77

Define deltaGº in terms of the equilibrium constant. Why is using Keq not a good idea? How can this be resolved?

Back 77

deltaGº=-RTln(Keq)

Once rxn starts, no longer in std conds, so use reaction quotient:
deltaG=deltaGº+RTln(Q)
where Q= ([C]^c[D]^d)/([A]^a[B]^b)
for aA + bB <-> cC + dD

Front 78

What is the specific heat of water in calories? Joules?

Back 78

1 cal, 4.184 joules

Front 79

What will be the sign of deltaG for:
H2O(l) + heat --> H2O (g)

Back 79

Entropy will increase if T*deltaS>H, but is only true at T>100ºC (below this, deltaG is positive)

Front 80

What will be the sign of deltaG for:
2C6H6(l) + 15O2(g) --> 16CO2(g) + 6H2O(g) + Heat

Back 80

Heat is released so deltaH is negative
Increase in S (TdeltaS is positive)--2 gases have higher entropy than 1 gas and 1 liq

thus delta G is (-) and rxn is spont

Front 81

deltaHrxn = ?

Back 81

SumdeltaHprods-SumdeltaHreacts

Front 82

For:
N2(g)-->2N(g), deltaHºrxn=954.2kJ

What is deltaH of nitrogen?

Back 82

deltaHrxn=954.2=2*(deltaHN)-(deltaHN2)
deltaHN2=0 because N2 is in elemental state

thus 2deltaHN=945.2 then solve

Front 83

If deltaG is negative, can work be done?

Back 83

Yes, energy released can be coupled to less favorable reactions.

Front 84

What is the specific heat of water in calories? Joules?

Back 84

1 cal, 4.184 joules

Front 85

For:

Br(g) + 5F(g)-->BrF5(g)

deltaHrxn=?

Back 85

deltaHrxn=SumdeltaHfProds-SumdeltaHfReacts

No bonds broken, so
=deltaHf(BrF5)-(deltaHf(Br)+5*deltaHf(F))

Front 86

Liquid/solid phase aka?

Back 86

Condensed phases

Front 87

Define miscibility.

Back 87

Degree to which 2 molecs mix

Front 88

Define emulsion.

Back 88

When two immiscible molecs placed under extreme conds to form homogenous mixture called emulsion (but are mixtures of discrete particles too small to be seen distinctly)

Front 89

What is the main component of a solid's KE?

Back 89

Vibrational energy

Front 90

Describe the two main classes of solids.

Back 90

Crystalline: ordered 3-D geometric arrangement of atoms (NaCl)

Amorphous: no ordered arrangement, but molecs fixed in place (glass)

Front 91

Describe ionic crystals.

Back 91

Aggregates of charged ions, high Tmelt, high Tboil (due to strong ESF b/t ions), poor conductors as solisd

Front 92

Describe metallic solids.

Back 92

High Tmelt, High Tboil (due to strong covalent bonds)

Front 93

What are the three unit cells of crystals?

Back 93

Simple cubic (cube)
Body-centered cubic (middle atom in cube center)

Face-centered cubic (atoms between every dimension)

Front 94

Define vapor pressure.

Back 94

Once vaporization adn condensation in equilibrium, pressure exterted by gas = vapor pressure, increases with Temp

Front 95

Under what conditions is boiling point reached.

Back 95

When Pvapor = Pexternal

Front 96

How do pure crystals differ from amorphous solids in melting points?

Back 96

Pure crystals have sharp, distinct T melt, whereas amorphous melt over larger range of temp due to less-ordered molecular distribn

Front 97

Define sublimation.

Back 97

s-->g

Front 98

Define deposition.

Back 98

g-->s

Front 99

Draw a single component phase diagram and label each phase's region, the triple point, freezing and critical point.

Back 99

Draw leaning Y on side to the right.
Going CW from top left:
Solid, Liq, Gas
TP at point where all meet
Critical Point as top right
Freezing point at midleft

Front 100

What is the triple point?

Back 100

Temp and P where all three phases in equilibrium

Front 101

What is the critical point?

Back 101

Above this T&P, cannot dx/dy b/t liq and gas

Front 102

Define colligative properties.

Back 102

Physical props derived solely from particles present, not on their nature

Front 103

Under what conditions does freezing point depression occur? How can it be calculated?

Back 103

When solute particles interfere with crystal formation.

deltaTf=Kf*m
Kf = constant
m = molality (mol solute/kg solvent)

Front 104

Under what conditions does boiling point elevation occur? How can it be calculated?

Back 104

Liquids boil when Pvapor=Patm; if Pvapor soln<Pvapor solvent, need higher T to boil.
deltaTb=Kb*m

Front 105

What is the equation for osmotic pressure?

Back 105

Pi=MRT
M = molarity of soln
Higher [soln]-->HIgher Pi

Pi depends only on amt of solute, not on its ID

Front 106

What does Raoult's Law state?

Back 106

IF solute B is added to pure solvent A, the original vapor pressure of A decreased by

deltaP=PstdofA-PofA=XofB*PstdofA

Where Xb = mole fraction of solute B in solvent A

Also, since Xb=1-Xa
Pa=Xa*PstdA
Pb=XbPstdB

Front 107

Given 117g NaCl dissolved in 1L H2O. What is the soln's molarity?

Back 107

Molarity=mol solute/L soln
=2mol/1L * 2 = 4molar because Na+ and Cl- dissociate in solution

Front 108

Define a homogenous solution.

Back 108

When mixtures of substances combine to form a single phase (generally a liquid)

Front 109

Describe solvent and solute.

Back 109

Solvent: component whose pahse remains same after mixing
SOlute molecs move about freely in solvent and can interact with other molecs/ions

Front 110

When does solvation occur?

Back 110

When attractive forces between solute and solvent are stronger than those between solute particles. Like dissolves like.

Front 111

Under what conditions is a solution dilute? Concentrated?

Back 111

Dilute: amt solute<<amt solvent
Concentrated: large proportion of solute:solvent

Front 112

What are the 7 rules of solubility?

Back 112

1. All alkali metals soluble
2. All ammonium ion (NH4+) salts soluble
3. All Cl-, Br-, I- salts soluble except (Ag+, Pb2+, Hg2+)
4. All sulfate ion salts (SO4 2-) soluble (except Ca+, Sr2++, Ba2+, Pb2+)
5. All metal oxides, except of alkali metals, CaO, SrO, BaO, are insoluble
6. All hydroxides, except of alkali metals, Ca++, Sr++, Ba++ INSOLUBLE.
7. All carbonates (CO32-), Phosphates (PO43-), sulfides (S2-), Sulfites (SO32-) are INSOLUBLE except those of alkali metals and ammonium

Front 113

What suffixes correspond to charges of the lesser and greater charge formed by a cation?

Back 113

-ous (lesser +)
-ic (greater +)

Front 114

What prefixes and suffixes correspond to the polyatomic anions containing different amounts of oxygen.

Back 114

Suffix: -ite = less, -ate=more
Prefix: Hypo = less, per = more
Ex: hypo-ite, -ite, -ate, per-ate

Front 115

If an anion adds protons to reduce charge, what prefixes/suffixes can be used?

Back 115

Can say hydrogen -ate, or bi-ate

ex: hydrogen carbonate vs Bicarbonate or for H2PO4: dihydrogen phosphate

Front 116

Define an electrolyte. When does an electrolyte classify as strong? Weak? Give examples.

Back 116

Solute whose solns are conductive

Strong: dissociates completely into constituent ions (NaCl, KI), like ionic cmpds/cmpds with highly polar covalent bonds (HCl)

Weak: ionizes incompletely and only some of solute present in ionic form in soln (acetic acid, weak acids, ammonia, weak bases, HgCl2)

Front 117

Define a nonelectrolyte. Provide an example.

Back 117

Do not ionize in soln, usually nonpolar gases/organic cmpds (O2, sugar)

Front 118

Why do electrolytes produce larger effects on colligative properties than could be expected from their given concentration?

Back 118

Electrolytes ionize in soln and will produce a larger effect

Front 119

What is the formula for determining percent composition by mass of a solution?

Back 119

mass solute/mass soln * 100

mass soln = mass solute + mass solvent

Front 120

What is the formula for determining the mole fraction of a solute?

Back 120

#mol cmpd/total #mol of all spp

Sum of all mol fracs=1

Front 121

Define molarity (which m?)

Back 121

molarity = M = #moles solute/L soln

Front 122

Define molality (which m?)

Back 122

#mol solute/kg solvent

Front 123

Define normality.

Back 123

N = #GEW solute/Lsoln
where GEW m<reactive capacity of solute

Need to know what purpose solution is being used for in order to determine GEW solute

Front 124

Equation for determining dilution?

Back 124

miVi=mfVf

works for any unit of concentration!

Front 125

Under what conditions is solution equilibrium achieved?

Back 125

When rate pptation=rate dissocn

Front 126

For A(m)B(n)(s)<-->mA^n+(aq) + +nB^m-(aq)

What is the ion product?
Solubility product constant?

Back 126

IP = [A^n+]^m*[B^m-]^n
Ksp=[A^n+]^m*[B^m-]^n

IP = Qsp when not in equilibrium

Front 127

How do the values of IP and Ksp relate to one another in terms of solution saturation?

Back 127

IP = Ksp }Soln saturated (at equil)
IP>Ksp } soln supersaturated and unstable; if disturbed (add more solute), will ppt until IP=Ksp

IP<Ksp} soln unsaturated, no ppt forms

Front 128

If solubility of Fe(OH)3=4.5E^-10mol/L What is the Ksp for Fe(OH)3?

Back 128

Fe(OH)3(s)<-->Fe3+(aq) + 3OH-(aw)
Ksp=[Fe3+][OH-]^3
[Fe3+]=4.5E^-10
[OH-]=3[Fe3+]
Ksp=(4.5E-10)[(3)(4.5E-10)]^3
=1.1 E-36

Front 129

Describe the common ion effect.

Back 129

Solubility of salt decreased when dissolved in solution already containing one of its ions, rather than in a pure solvent.

Front 130

IF Ksp of AgI(aq)=1E-16mol/L, and a 1E-5M soln AgNO3 is saturated with AgI, what is the final concentration of I?

Back 130

AgI(s)<-->Ag+(aq)+I-(aq)
Ksp=[Ag+][I-]
1E6-16=1E-5[I-]
[I-]=1E^-11mol/L