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MCAT Comprehensive > Gen Chem Review > Flashcards

Gen Chem Review Flashcards

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MCAT flashcards
1
Q

What are the three fundamental particles of matter, and which determines the identity of an element?

A

Protons, neutrons, and electrons

Protons determine the identity of an element

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2
Q

Isotopes differ by the number of which fundamental particle?

The mass number of an element is determined by which two particles?

A

Isotopes differ by the number of neutrons

The mass number is determined by the number of protons and neutrons

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3
Q

What letter stands for the principal quantum number?

What is the range of possible values of this number?

A

n = 1 to n = infinity

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4
Q

What are the three rules of electron filling

A

Fill lower energy levels and sublevels before adding electrons to higher energy levels

There is a maximum number of two electrons per orbital, and they must have opposite spins

Half fill orbitals of equal energy before pairing electrons in any one orbital in a given subshell

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5
Q

What are the three properties of electromagnetic radiation?

A

Frequency, wavelength, and energy

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6
Q

Define quantized

A

Something is quantized if it only comes in certain discrete sizes

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7
Q

Name the three types of decay from least to most damaging

A

Alpha, beta, gamma

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8
Q

What are three types of covalent bonds?

A

Normal (polar or nonpolar)

Metallic

Coordinate covalent (Transition metals)

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9
Q

Give two other names for Lewis bases

A

Ligand (an ion or molecule that binds to a central metal atom to form a coordination complex)

Nucleophile

Chelator

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10
Q

Name the various intermolecular forces from strongest to weakest

A

Hydrogen bonds > dipole-dipole > London Disperson

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11
Q

When energy is added to a substance, that energy can be used to do one of two physical things. What are they?

A

Increase the temperature (Increase KE)

Cause a phase change (Increase PE)

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12
Q

What two things does vapor pressure depend on?

A

Temperature and intermolecular forces

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13
Q

When does a liquid boil?

A

When the vapor pressure of the liquid = atmospheric pressure

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14
Q

The phase of a substance depends on what two properties besides intermolecular forces?

A

Temperature and pressure

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15
Q

What assumptions do we make about ideal gases?

A

Ideal gases are composed of molecules that take up no volume and experience no intermolecular forces

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16
Q

What do constants a and b account for in Van der Waal’s equation for real gases?

A

a accounts for the intermolecular forces between gas molecules

b accounts for the molecular volume of the gas particles

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17
Q

What conditions are indicated at STP

A

1 atm and 0 degrees Celsius

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18
Q

What is the volume of 1 mole at STP

A

22.4 L

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19
Q

Describe at the molecular level what happens to a solid when it dissolves

A

Solute particles are separated and encapsulated by solvent molecules such that the solute is observed to dissole

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20
Q

Define electrolyte

A

An electrolyte is a solute that dissociates into charges particles in solution

(i value is > 1)

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21
Q

What is the difference between an intermediate and a transition state?

A

Intermediates are found at local energy minima along a reaction coordinate while transition states are at local energy maxima along the reaction cordinate

Transition states the highest energy species in a reaction because bonds are breaking and forming, so it cannot be isolated from a reaction

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22
Q

What are two ways to determine a rate law?

A
  1. a multi-trial experiment in which is the concentration of each reagent is changed at a time
  2. Looking at the rate-determining step in a previously proposed mechanism
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23
Q

What three properties affect the rate of a reaction?

A

Concentration (or for gases, partial pressure), temperature, and activation energy

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24
Q

What does it mean for a reaction to be at equilibrium?

A

The rate of the forward reaction is equal to the rate of the reverse reaction

or

The concentrations of reactants and products do not change with respect to time

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25
Q

What types of substances are included in the equilibrium (K) expression, and what types of substances are excluded?

A

Gases and aqueous species are always included

Pure liquid and solids are not included

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26
Q

State three ways to disturb or stress a chemical equilibrium

A

Change the concentration of reactions or products, change the temperature, or change the volume of the container, thereby changing the pressure

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27
Q

What is the only way to change the equilibrium constant , K?

A

Change the temperature

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28
Q

Name the strong acids and strong bases

A

Strong acids = HCl, HBr, HI, HNO3, HClO4, H2SO4

Strong bases = Group 1 hydroxides and oxides; Ba/Sr,Ca hydroxides, and metal amides

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29
Q

Define conjugate pair

A

Two molecules or ions that differ by one H+

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30
Q

How is the pH of a strong acid calculated?

A

pH = -log [H+]; which is the same as -log[acid], since strong acids completely dissociate

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31
Q

Give three reasons why a titration might be performed

A

To determine the concentration of an unknown acid or base

To create a buffer

To determine the pKa or pKb of an unknown weak acid or weak base, and perhaps thereby identify the acid or base as well

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32
Q

What is the equivalence point of a titration?

A

The equivalence point has been reached when the same number of moles of an acid and base have been mixed

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33
Q

What is a buffer?

A

A solution that minimizes the impact of the addition of an acid or base on the pH of the solution.

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34
Q

What happens to the pH of a buffer when it is diluted? Concentrated?

A

The pH does not change upon the addition or removal of solvent as the relative concentrations of the acid and conjugate base in solution change proportionately; so their ratio does not change

35
Q

Identify the standard state conditions for temperature and pressure

A

T = 25 degrees C

P = 1 atm

36
Q

When is the entropy of a substance equal to zero?

A

When a pure element is solid at 0 K

37
Q

Which process requires energy, breaking a bond or forming one?

A

Breaking bonds is endothermic

Forming bonds is exothermic

38
Q

What does a positive reduction potential indicate?

A

The reduction half-reaction is spontaneous, while the associated oxidation half-reaction is nonspontaneous

39
Q

Which electrochemical cell type produces electricity from a spontaneous chemical reaction, an electrolytic cell or a galvanic cell?

A

Galvanic cells use spontaneous reactions to produce electricity, while electrolytic cells use electricity to force nonspontanous reactions to occur

40
Q

What is the sign of an electrode in a galvanic cell? An electrolytic cell?

A

In a galvanic cell, the cathode is positive and the anode is negative

In an electrolytic cell, the signs are reversed

41
Q

Give two examples of elements that do not obey the Aufbau principle

What are their electron configurations?

A

Chromium (Cr) and its family members or Copper (Cu) and its family members

Electron Configurations:

Cr = 3d54s1

Cu = 3d104s1

42
Q

Which electrons do transition metal atoms lose first when ionized?

A

Valence s electrons

43
Q

What is the difference between paramagnetic and diamagnetic elements, and give an example of each

A

Paramagnetic elements have unpaired electrons (N)

Diamagnetic elements have all of their electrons paired (Ne, or any element with a filled orbital shell)

44
Q

What happens to the spacing between successively higher energy levels in an atom as you move farther from the nucleus?

A

It decreases

45
Q

Describe each kind of nuclear decay

A

D = nucleus emits helium nucleus (two protons and two neutrons

B- = a neutron converts into a proton and an electron is created and emitted

B+ = a proton convets into a neutron and a positron (e+ which is emitted)

EC = a proton in the nucleus captures an inner-shell electron and converts into a neurton

Gamma = an exctied nucleus drops to a lower energy state by emitting a gamma photon

46
Q

What type of mathematical relationship is associated with all types of radioactive decay?

A

Radioactive elements decay exponentially with respect to time.

47
Q

Why is the mass of a necleus not equal to the mass of the individual protons and neutrons that compromise it?

A

The binding energy that is released when nucleons are bound together in the nucleus comes from the mass defect according to E = mc2

48
Q

Define each periodic trend

A

Atomic radius is the extent of the valence eelectrons of an atom

Ionization energy is the energy required to remove a mole of valence electrons from a mole of gaseous atoms of a given element

Electron affinity is the energy associated with added a mole of electrons to the valence shell of a mole of gaseous atoms of a given element

Electronegativity is the measure of the amount of pull an atom has on shared valence electrons in a bond

Acidity is the tendency of a molecule to give up a hydrogen ion

49
Q

Which three periodic trends follow the same pattern?

Why do they all agree?

A

First ionization energy, electron affinity, and electronegativity

They are all inversely related to atomic size, and thus all follow the opposite trend from atomic size

50
Q

What charge is generally associated with larger ions? Smaller ions?

A

Generally, negative ions are larger and positive ions are smaller (Than a neutral atom)

51
Q

Name at least three properties of liquids that depend on intermolecular forces

A

Solubility, vapor pressure, boiling point, melting point, viscosity, surface tension

52
Q

What quantity is specified by the average kinetic energy of the molecules of a substance?

A

Temperature

53
Q

In which phase do molecules have the most energy?

A

Gas phase (If plasma is ignored)

54
Q

At a given temperature, which gas molecules travel faster, those with small molecular weights or large ones?

A

Gases with smaller molecular weights travel faster

55
Q

State the sign ∆H and ∆S for each of the six phase changes, and rank them from highest magnitude to lowest

A

∆Hsub > ∆Hvap > ∆Hfus > 0

The others are negative: Absolute values of ∆Hdep > ∆Hcond > ∆Hfreez

∆Ssub > ∆Svap > ∆Sfus > 0

The others are negative: Absolute values of ∆Sdep > ∆Scond > ∆Sfreez

∆Hsub/∆Ssub = Absolute value of ∆Hdep/∆Sdep

Same goes for all opposing phase changes

56
Q

What happens at the molecular level when a substance changes phase

A

Intermolecular forces are formed or broken

57
Q

What is usually the densest phase of matter?

A

Solid, the main exception being water, which is most dense in its liquid phase

58
Q

Give an example of gas that most approaches ideal behavior

A

Helium

59
Q

What temperature and pressure conditions allow a gas to behave most ideally?

A

High temperatures and low pressures (or large volumes)

60
Q

What happens to the solubility of solids in liquids as the temperature is increased? Why does this happen?

A

Solubility increases at higher temperatures because the solute-solute intermolecular forces weaken as solute molecules spread out due to increased vibration

61
Q

How does the solubility of gases and liquids depend upon temperature and pressure?

A

The solubility of gases decreases with increasing temperature, but increases with increasing pressure

62
Q

What ions always result in a soluble salt?

Which ions generally form insoluble salts?

A

Group I, ammonium (NH4+), nitrate (NO3-), acetate (C2H3O2), and bicarbonate salts are always soluble in water

Pb, Ag, and Hg salts are generally insoluble in water, unless paired with the anions previously mentioned.

63
Q

What does a catalyst do and how does it do it?

A

A catalyst increases the rate at which a reaction reaches equilibrium by lowering the activation energy

64
Q

What does the order of the rate law say about the reaction mechanism?

A

The number of molecules colliding in the rate-determining step

65
Q

How will a catalyst affect a system that is at equilibrium?

A

It won’t do anything, as a catalyst only helps a reaction get to equilibrium more quickly by increasing the reaction rate

66
Q

How does the rate of a chemical reaction change with temperature?

A

Reaction rate always increases with increasing temperature

67
Q

How does the reaction quotient Q help determine if a reaction is at equilibrium?

A

If K = Q, the reaction is at equilibrium

If K < Q, the reaction will proceed in the reverse direction to reach equilibrium

If K > Q the reaction will proceed in the forward direction to reach equilibrium

68
Q

What does the term strong mean in relation to an acid/base/electorlyte? What about the term weak?

A

Complete dissociation K > 1; Partial dissociation K < 1

All soluble salts are strong electrolytes, as are strong acids and strong bases

Weak acids and weak bases are weak electrolytes (they do not completely dissociate)

69
Q

What equilibrium exists in water that is shifted by the addition of an acid or base, and what is the value of K for this reaction at standard conditions?

A

The autoionization of water Kw = 10-14 at standard conditions (1 atm/ 25 C)

70
Q

What two pieces of information are needed to calculate the pH of a weak acid?

A

[H+] = √(Ka)x[HA]

HA = concentration of the acid

71
Q

What information is needed to predict the pH at the equivalence point of a titration?

A

The strengths of the acid and base being mixed

At the equivalence point, pH = 7 if a strong acid is mixed with a strong base

pH < 7 if a strong acid is mixed with a weak base

pH > 7 if a strong base is mixed with a weak acid

72
Q

Describe two ways to make a buffer

A
  1. Add roughly equal molar amount of a weak acid and a salt of its conjugate base (or a weak base and the salt of its conjugate acid)
  2. Neutralize half of a sample of weak acid (or weak base) by a strong base (Or strong acid)
73
Q

How is the pH of a buffer calculated?

A

Using the Henderson-Haselbach equation

pH = pKa + [conjugate base]/[acid]

74
Q

When does the pH = pKa for a buffer?

What is this point called in titration?

A

When the concentrations of the weak acid and its conjugate base are equal

This occurs at the half-equivalence point in a titration experiment

75
Q

How are the common ion effect and the mechanism of a buffer related?

A

They are the same thing, an application of Le Chatlier’s Principle

Common ion effect = refers to the decrease in solubility of an ionic precipitate by the addition to the solution of a soluble compound with an ion in common with the precipitate.

76
Q

What is the enthalpy of formation?

A

The amount of energy associated with forming one mole of a compound from its constituent elements in their standard states

77
Q

What three things must be considered to determine whether a reaction will happen, or be spontanous

A

Change in enthalpy, change in entropy, and temperature

78
Q

What kind of reaction occurs at the anode of an electrochemical cell?

At the cathode?

A

Oxidation occurs at the anode

Reduction occurs at the cathode

79
Q

Describe the state of a reaction at ∆G = 0

A

The reaction is at equilibrium

80
Q

What is the sign of a cell voltage in an electrolytic cell?

A

Negative

81
Q

What is the purpose of a salt bridge in a galvanic cell?

A

To prevent charge separation as electrons move from one chamber to the other. The salt bridge maintains charge neutrality in each chamber.

82
Q

What are the common labels for a curve of a redox titration?

A

The y-axis is normally E, electrical potential in volts

The x-axis is normally the amount of tritant added in mL

83
Q

What information is required to calculate the amount of an element that can be produced by an electrolytic cell?

A

The current (in amps), the amount of time the current is applied, Faradays constant, the moles of electrons transferred per mole of the element formed (given by the half reaction)

MCAT Comprehensive (10 decks)

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