Mcat General Chemistry Review

Front 1

Isotopes of hydrogen names

Back 1

protium, deuterium, tritium

Front 2

Bohr model

Back 2

electrons travel in specific orbits at specific energy levels around dense, positive nucleus.
(doesn't account for electron-electron interactions)

Front 3

Quantum Mechanical Model concepts

Back 3

A quantum = Energy difference between energy levels.
Model has electrons moving in orbitals, the areas where you are most likely to find an electron. (≥ 1 e⁻)

Front 4

Heisenberg uncertainty principle states...

Back 4

impossible to know both an electron's position and momentum at same time

Front 5

Hund's rule states...

Back 5

electrons prefer to be unpaired with parallel spins.

Front 6

Key eqn to determine energy value of a quantum.

Back 6

E = hf
E = Energy (J)
h = Planck's constant (J·s)
f = frequency of radiation (1/s)

Front 7

Quantum numbers

Back 7

n (principal) — holds 2n² e⁻s max
l (azimuthal / angular p) — = n-1, holds 4l+2 e⁻ max
m(l) (magnetic) — = -l to +l, id's spec orbital, 2l + 1 possible values
m(s) (spin) — +½ or -½

l determines s, p, d, etc. subshells

Front 8

Electron Subshell Flow Diagram

Back 8

1s
2s 2p
3s 3p 3d
...

Front 9

paramagnetic vs. diamagnetic

Back 9

para = unpaired e⁻s ∴ attraction
dia = all paired e⁻s ∴ repulsion

Front 10

Key eqn to determine energy of an electron.

Back 10

E = -R(h) / n²
Use this eqn also to determine E of emitted photon!
E = energy
R = Rydberg constant
n = principal quantum number

Front 11

Key eqn to determine electromagnetic energy.

Back 11

E = hc / λ
E = energy
h = Planck's constant
c = speed of light
λ = wavelength

Front 12

Ionization energy

Back 12

E to remove an e⁻

Front 13

Electronegativity

Back 13

How much an atom wants to keep an e⁻

Front 14

Starting rule for drawing Lewis structures.

Back 14

Generally least electronegative atom is at center.

Front 15

How to determine formal charge. (eqn)

Back 15

Formal charge = V - N(nonbonding) - ½N(bonding)
V = normal number of e⁻s in valence shell
N(nonbonding) = nonbonding electrons
N(bonding) = bonding electrons

Front 16

Electronic vs. molecular geometry.

Back 16

electronic = arrangement of electrons
molecular = shape

Front 17

**STP vs. standard state**

Back 17

STP = 0°C, 1 atm
standard state = 25°C, 1 atm

Front 18

Key eqn to determine kinetic energy or velocity of a gas from temperature.

Back 18

KE = ½mv² = 3/2 kT
k = Boltzmann constant
T = temperature of a gas

Front 19

Key eqn to determine relative rates of diffusion or effusion of a gas. Used to compare velocity of or distance traveled by 2 gases at same temp.

Back 19

Graham's Law
r₁ / r₂ = √(M₂ / M₁)
r = diffusion rates of 2 gases
M = molar masses of 2 gases

Front 20

Density

Back 20

mass / volume
For gases: g/L

Front 21

Volume of a gas at STP

Back 21

22.4 L/mol

Front 22

Key eqn to determine total pressure of a bunch of gases.

Back 22

Dalton's Law of partial pressures.
P = P₁ + P₂ + P₃ ...
P₁ = PX₁
X₁ = n₁ / n
X = mole ratio
n₁ = moles of gas 1
n = moles total of gases
P = total pressure

Front 23

Avogadro's number

Back 23

6.022 e23

Front 24

Normality measure.

Back 24

Measure of concentration. (equivalents / L)

Front 25

Empirical vs. molecular formulas.

Back 25

empirical = simplest whole number ratio
molecular = numbers of atoms of each element in actual molecule

Front 26

Eqn to determine percent composition by mass.

Back 26

% composition = mass of X in formula / formula weight) *100

Front 27

5 types of chemical reactions

Back 27

Combination (reactants > products)
Decomposition (reactants < products)
Single-Displacement (redox rxns)
Double-Displacement/Metathesis (often 2 reactant halves forming precipitate or gas)
Neutralization (Acid + B: → salt)

Front 28

spectator ions

Back 28

ion in a rxn we can ignore b/c it's not doing anything
Removal ➔ net ionic eqn

Front 29

Measuring ionic vs. covalent compounds

Back 29

ionic = formula weights
covalent = molecular weights

Front 30

gram equivalent weight

Back 30

measure of mass of a substance that can donate one equivalent of a species of interest

e.g. gram equivalent wt of acid? How many H's to donate? divide by molecular weight

Front 31

Key eqn used for experimental determination of the rate law or to calculate a rate from given rxn data.

Back 31

Rate = k [A]ˣ [B]ʸ
k = rate constant
[ ] = concentration of substrate
x = orders of the rxn
x+y = overall rxn order

Front 32

Only cases where you can take stoichiometric coefficients for use in determining rxn order.

Back 32

1. Rxn mech is a single step
2. Complete rxn mech given and rate-determining step indicated.

Front 33

Reaction orders

Back 33

Zero order (rate only affected by catalysts & temp Δ)
rate = k [A]⁰ [B]⁰ = k
First order (ex: radioactive decay)
[Aᵀ] = [A₀] e⁻ᵏᵗ ≡ conc. of radioactive substrate at time t
Second order (often suggests physical collision)

Front 34

Enthalpy Δ

Back 34

ΔH = difference bw potential E's of products & reactants
-ΔH = exothermic = releases heat (product)
+ΔH = endothermic = heat absorbed (reactant)

Front 35

Factors that affect rxn rate

Back 35

[Reactant] (except for zero-order)
Temp
Medium
Catalysts (homogeneous = same phase as reactant vs. heterogeneous)

Front 36

Key eqn to determine the constant ratio of products to reactants of a system at equilibrium.

Back 36

Law of Mass Action
For rxn aA + bB → cC + dD
K(eq) = ( [C]ᵓ [D]ᵈ ) / ( [A]ª [B]ᵇ )
K(eq) = k₁ / k₋₁

Front 37

Key eqn to determine if a rxn is at equilibrium and if not, which direction it will proceed.

Back 37

The Reaction Quotient
For rxn aA + bB → cC + dD
Q𝔠 = ( [C]ᵓ [D]ᵈ ) / ( [A]ª [B]ᵇ )
For comparison to K(eq) (what it would be if at equilibrium).
Q𝔠 < K(eq), ΔG < 0 ➔ proceeds forward to equilibrium
Q𝔠 > K(eq), ΔG > 0 ➔ proceeds in reverse to equilibrium

Front 38

Method/Eqn to determine K(sp) of a salt.

Back 38

1. Split the salt into ions. Ksp = [+][+]..[-]..
2. Multiply number of ions by the molar solubility.
3. Plug back into eqn for ion concentration (Ksp = [+]²[-]) and solve for Ksp.

Front 39

Characterizations of systems with exchange w/surroundings (or ∅).

Back 39

Isolated (∅ xΔ)
Closed (xΔ of E (heat & W) but ∅ matter)
Open (heat, W, and matter xΔ)

Front 40

Types of processes with constants.

Back 40

Adiabatic = ∅ xΔ of heat bw system & environment
Isothermal = ∅ Δ in temp in system

Front 41

Key eqn to determine E txfer to/from a system.

Back 41

(Most common with gases)
ΔU = Q - W
U = internal E of a system
Q = heat txfer'd (+ endothermic, - exothermic
W = work

Front 42

2 Basic Types of Calorimetry

Back 42

Constant-pressure
Constant-volume
(bomb calorimeter - ∅W done b/c W = PΔV & no heat txfer'd ∴ Q = 0, so no xΔ of heat/W/matter & no internal EΔ (ΔU = 0) ADIABATIC)

Front 43

Key eqn to determine temperature after heat txfer. (Calorimetry probs!)

Back 43

Specific heat
q = mcΔT ("q equals MCAT")
q = heat absorbed/released in process
m = mass
c = specific heat
ΔT = change in temp

Front 44

Key eqn to determine enthalpy change.

Back 44

(Most common for determining whether rxn is exo- or endothermic)
ΔH = H(products) - H(reactants)
+ = endo
- = exo

Front 45

Eqn to calculate entropy in a reversible process.

Back 45

ΔS = Q(rev) / T
ΔS = Entropy (usually kJ/mol·K)
Q(rev) = heat gained/lost in a reversible process
T = Temperature in °K

Front 46

Key eqn to determine change in free energy, commonly to determine whether rxn is spontaneous or not.

Back 46

Gibbs Free Energy
ΔG = ΔH - TΔS ("Get High Test Scores!")
ΔG = measure of Δ as system undergoes a process
ΔH = enthalpy
T = temp (K)
ΔS = entropy
∅ effect on speed, just on whether or not rxn happens

Front 47

Key concept regarding signs of ΔH and ΔS.

Back 47

Temp dependent when both ΔH & ΔS have same sign.
Both + ≡ spontaneous only at high temps
Both - ≡ spontaneous only at low temps

Front 48

Key eqn to determine change in free energy with respect to K(eq), commonly to determine a reaction's spontaneity.

Back 48

Gibbs Free Energy
ΔG° = -RT ln(K(eq))
ΔG° = Standard free energy change
R = gas constant (≈8 J/K·mol)
K(eq) = equilibrium constant

Front 49

Eqn to replace K(eq) with a system not at equilibrium.

Back 49

Q = ( [C]ᵓ [D]ᵈ ) / ( [A]ª [B]ᵇ )

Front 50

Key eqn to determine change in free energy with respect to standard free energy and Q, commonly to determine the spontaneity of a rxn at a pt of non-equilibrium.

Back 50

Gibbs Free Energy
ΔG = ΔG° + RT lnQ
ΔG = RT ln(Q/Kᵉ)
Kᵉ = K equilibrium, equilibrium constant
Q = reaction quotient
If Kᵉ < Q = non-spontaneous
If Kᵉ > Q = spontaneous

Front 51

Laws of thermodynamics & associated eqns.

Back 51

0. Zeroth Law (a = b & b = c, then a = c w/ thermal equilibriums)
1. E is conserved
2. Spontaneous evolution towards equilibrium (w/ greatest entropy possible)
3. ΔS➔0 as °K➔0

Front 52

Packing forms of metallic solids

Back 52

Simple cubic
Body-centered cubic
Face-centered cubic (NaCl 6:6)

Front 53

Mixing liquids

Back 53

mixable liquids = miscible
non-mixable = immiscible
small non-mixable particles mixed = emulsion

Front 54

Phase changes

Back 54

solid to gas — sublimation
gas to solid — deposition
solid to liquid — fusion, melting
liquid to solid — freezing, solidification, crystallization
gas to liquid — condensation
liquid to gas — vaporization

Front 55

Phase Diagram

Back 55

"Cup holds the liquid, solid pushes over the cup, only air beneath"
y-axis = Pressure
x-axis = Temperature
critical pt = above which, no distinction bw gas and liquid, heat of vaporization = 0

Front 56

Colligative properties

Back 56

(all dependent on concentration of dissolved particles rather than what was dissolved)
vapor pressure depression
boiling point elevation
freezing point depression
osmotic pressure

Front 57

Key eqn to calculate vapor pressure depression & plot phase diagram for solution of two liquids. (usually in reference to distillation)

Back 57

Raoult's Law (for ideal solutions)
Pᴬ = XᴬP°ᴬ
Pᴬ = partial pressure of component A
Xᴬ = mole fraction of solvent A in solution
P°ᴬ = vapor pressure of pure solvent A
Law works best when solute-solute, solvent-solvent, and solute-solvent interactions are all very similar.
When solute-solvent rxn weak, vapor P↑. (more evap)
When solute-solvent rxn strong, vapor P↓. (less evap)

Front 58

Key eqn to calculate boiling point elevation given molality or molality given bp.

Back 58

ΔTᵇ = iKᵇm
ΔTᵇ = boiling point elevation
i = van't Hoff factor = mol particles dissolved / mol solute molecules
Kᵇ = proportionality constant of solvent (given)
m = molality (mol solute / kg solvent)

Front 59

Key eqn to calculate freezing point depression given molality or molality given fp depression.

Back 59

ΔT𝑓 = iK𝑓m
ΔT𝑓 = freezing point depression
i = van't Hoff factor (mol particles solute / mol molecules solute)
K𝑓 = proportionality constant of solvent (given)
m = molality (mol solute / kg solvent)

Front 60

Key eqn to calculate osmotic pressure from molarity or vice versa.

Back 60

Π = iMRT
Π = osmotic pressure
i = van't Hoff factor (mol particles dissolved / mol molecules solute)
M = molarity of soln
R = ideal gas constant (≈8)
T = temperature (in K)

Front 61

What is an ideal solution?

Back 61

Enthalpy (ΔH) = 0 (or approaches it)
(strength of new interactions w/solute ≈ strength of original interactions)

Front 62

Solubility concepts

Back 62

solubility = max amt of substance that can be dissolved in a particular solvent at a particular temp
saturated = max added
dilute vs. concentrated
sparingly soluble salts = don't dissolve well in H₂O

Front 63

*7 general solubility rules

Back 63

1. All salts of alkali metals are H₂O soluble.
2. All salts of the ammonium ion (NH₄+) and nitrate (NO₃⁻) are H₂O soluble.
3. Cl+, Br+, I+ are H₂O soluble unless w/Ag+, Pb²+, Hg₂²+
4. SO₄²+ are H₂O soluble except Ca²+, Sr²+, Ba²+, Pb²+
5. CaO, SrO, BaO are H₂O soluble
6. Ca(OH)₂, Sr(OH)₂, Ba(OH)₂ are H₂O soluble
7. Everything else, H₂O INsoluble.

Front 64

Ion nomenclature
-ous vs. -ic?
-ide?
-ite & ate?

Back 64

-ous (lesser charge) vs. -ic (greater charge)
-ide (monatomic anions)
-ite (oxyanion w/less O) & -ate (oxyanion w/more O)

Front 65

Ways of expressing concentration.

Back 65

% Composition by mass (100 * kg solute / kg solution)
Mole fraction (mol solute / mol solution)
Molarity (mol solute / L solution)
Molality (mol solute / kg solvent) (∵H₂O density = 1kg/L)
Normality (# equivalents solute of interest / L solution)
(equivalent = mole of charge)
Dilution (M₁V₁ = M₂V₂)

Front 66

Key eqn to determine K(sp) or molar solubility. (often in context of the ion product)

Back 66

Solubility Product Constant
For A₁B₂ ⇄ 1A²⁺ + 2B¹⁻,
K(sp) = [A²⁺]¹ [B¹⁻]²

Front 67

Key eqn to determine behavior of a solution by comparing IP to K(sp)

Back 67

I.P. = [A²⁺]¹ [B¹⁻]²
I.P. = Ion product (analogous to Q for chem rxns)
Q(sp) < K(sp) = unsaturated
Q(sp) > K(sp) = supersaturated

Front 68

Unconventional definition of boiling point

Back 68

When vapor pressure = atmospheric pressure, you get bp.

Front 69

Specific heat of H₂O

Back 69

c = 4.184 J / g·K = 1 cal / g·K

Front 70

Prob: What is molar mass of solute given mass solute, mass solvent, boiling point, and Kᵇ?

Back 70

Use equation ΔTᵇ = iKᵇm
where ΔTᵇ = change in boiling point temp
Kᵇ = constant for solvent bp
m = molality (mol solute / kg solvent)

Front 71

Prob: What is solubility of gas at a new atmospheric pressure? Given solubility at old atmospheric pressure.

Back 71

Solubility = New pressure % * solubility @ original pressure

e.g. 80% of 1 atm = .8 atm new * Orig P

Front 72

Formation rxns

Back 72

All of the reactants are in standard elemental state!

Front 73

What do catalysts affect?

Back 73

Do NOT affect equilibrium (K(eq))!
Only affect rate!