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Spring 2024 > Chem 2 Exam 1 > Flashcards

Chem 2 Exam 1 Flashcards

1
Q

What is an intramolecular force?

A
  • Bonds within a molecule.
  • Usually strong.
  • Determine the chemical properties
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2
Q

What is an intermolecular force?

A
  • Attraction between molecules.
  • Usually weak.
  • Determine the physical properties.
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3
Q

What are the types of intermolecular forces (IMFs)?

A
  1. London Dispersion Forces
  2. Dipole-Dipole Attraction
  3. Hydrogen Bonding
  4. Ion-Dipole Forces
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4
Q

What are London Dispersion Forces?

A
  • Operate between all species (neutral, charged, polar, or nonpolar).
  • Results from uneven distribution of electrons.
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5
Q

What do the strengths of London Dispersion Molecules depend on?

A
  • Size of molecules (molar mass)
  • Molecular shape (compact of elongated)
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6
Q

Effect of size on a large molecule (london dispersion)

A

Larger molecules —> more polarizable —> stronger london forces —> high MP, BP

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7
Q

Effect of size on small molecule (london dispersion)

A

Smaller molecules —> less polarizable —> weaker london forces —> low MP, BP

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8
Q

Compact molecular shape (london dispersion forces)

A
  • more compact
  • small area for interaction
  • weaker london forces
  • lower boiling point
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9
Q

Elongated molecular shape (london dispersion forces)

A
  • less compact
  • larger area for interaction
  • stronger london forces
  • higher boiling point
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10
Q

What is Dipole-Dipole Attraction?

A
  • occur only in polar molecules, which contain permanent dipoles
  • the positive end of one permanent dipole attracts the negative end of another through dipole-dipole forces
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11
Q

How to find polar molecules?

A
  • different atoms asymmetrically attached to central atom
  • only one lone pair on central atom
  • lone pairs are asymmetrically placed around the central atom
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12
Q

What is Hydrogen Bonding?

A
  • very strong special type of dipole-dipole interaction
  • occurs between H and F, O, or N
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13
Q

What are Ion-Dipole Forces?

A
  • Occurs when an ionic compound is mixed with a polar molecule
  • ions are attached to the dipole of polar molecules
  • higher the charge on ion, stronger ion-dipole interaction
  • smaller size of ion, stronger ion-dipole interaction
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14
Q

IMFs from strongest to weakest?

A
  • ion dipole forces
  • hydrogen bonding
  • dipole-dipole attraction
  • london dispersion forces
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15
Q

What are the three properties that depend on the strengths of intermolecular forces?

A
  1. Viscosity
    2 Surface Tension
  2. Capillary Action
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16
Q

What is Viscosity?

A

measures a liquids resistance to flow
- ex. liquid with lower viscosity flow freely (water, gasoline,…) liquid with higher viscosity do not flow freely (honey, syrup…)

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17
Q

What factors affect viscosity and why

A
  1. Intermolecular Forces - stronger IMFs = higher viscosity
  2. Temperature - higher temp = lower viscosity
  3. Size and Shape of Molecule - large and complex structure = higher viscosity
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18
Q

What is Surface Tension?

A

The tendency of liquids to minimize their surface area.
- liquid beads to yield the minimum surface are (surface molecule interacts with 4 neighbors while interior molecule interacts with 6 neighbors)

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19
Q

What Factors Affect Surface Tension and Why

A
  1. Intermolecular Forces - stronger IMFs = higher surface tension
  2. Temperature - surface tension decreases as temp increases
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20
Q

What is Capillary Action?

A

The rise of liquid in a narrow tube (i.e.a capillary) immersed in the liquid
- due to attraction of the liquid molecules to the surface of the tube
- the attraction to the surface draw the liquid up tube

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21
Q

What is Solid to Gas Called and Vice Versa?

A
  • Solid to gas = sublimation
  • gas to solid = deposition
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22
Q

Vaporization

A
  • liquid to gas
  • endothermic process
  • energy needed to overcome IMFs
  • ∆Hvap always positive
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23
Q

What is ∆Hvap Heat of Vaporization?

A

the amount of heat required to vaporize one mole of a liquid to gas

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24
Q

Condensation

A
  • gas to liquid
  • exothermic process
  • energy is released
  • ∆Hcond always negative
    ∆Hcond = −∆Hvap
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25
Q

Rate of Vaporization Increases with….?

A
  • Increasing Temp: average kinetic energy increases and more molecules have enough energy to over the IMFs
  • Increasing Surface Area: the surface molecules are held less tightly, thus have greatest tendency to evaporate
  • Decreasing Strength of IMFs: less attraction forces to hold molecules in liquid state
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26
Q

What is Dynamic Equilibrium?

A

Reciprocal processes are occurring at equal rates
- system at dynamic equilibrium: rate of forward reaction = rate of backward reaction
- occurs in closed systems where molecules cant escape
- the double arrow indicates dynamic equilibrium

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27
Q

What is Vapor Pressure?

A

pressure exerted by a vapor in equilibrium with a solid or a liquid at a given temperature in a closed system

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28
Q

What Affects Vapor Pressure of a liquid?

A
  • Temperature
  • IMFs
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29
Q

How does Temperature Affect Vapor Pressure?

A

At higher temps:
- molecules have higher thermal energy
- more molecules have enough energy to evaporate
- number of molecules in gas phase is higher
- vapor pressure is high
- INCREASING TEMPERATURE INCREASES VAPOR PRESSURE

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30
Q

How do IMFs Affect Vapor Pressure?

A
  • Weaker IMFs —> high vapor pressure
  • Stronger IMFs —> Low vapor pressure
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31
Q

What is Boiling Point?

A

Temperature at which liquids vapor pressure = the external pressure
- during boiling, temp is constant
- variations in atmospheric pressure will change boiling point (high altitude –> lower atmospheric pressure –> lower BP)

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32
Q

What is normal boiling point?

A

1 atm or 760 torr or 101.3 kPa

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33
Q

Effects of IMFs on Boiling Point

A
  • weak IMF —> higher vapor pressure —> low BP
  • strong IMF —> lower vapor pressure —> high BP
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34
Q

IMF, Rate of Vaporization, Vapor Pressure, and BP

A
  • Weak IMF —> Higher rate of vaporization —> high vapor pressure —> low boiling point
  • Strong IMF —> lower rate of vaporization —> low vapor pressure —> high boiling point
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35
Q

What does each symbol stand for in ln(P2/P1) = -∆𝐻vap/R (1/T2 - 1/T1) ?

A
  • P1 = vapor pressure at temp. 1
  • P2 = vapor pressure at temp. 2
  • ∆𝐻vap = heat of vaporization (J/mol)
  • R = gas constant, 8.314 J/mol x K
  • T1 = temp. 1 in kelvin
    T2 = temp. 2 in kelvin
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36
Q

What is a phase diagram?

A

Pressure(y) - temperature(x) graph
- shows the effects of both pressure and temp. on phase changes
- Three main regions: solid, liquid, gas

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37
Q

What is Triple Point (phase diagram)?

A

temp. and pressure where 3 phases coexist in equilibrium

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38
Q

What is Critical Point (phase diagram)?

A

highest temp. and pressure at which a pure material can exist in gas/liquid equilibrium
- CRITICAL POINT IS ALWAYS HIGHER THAN TRIPLE POINT

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39
Q

What is Supercritical Fluid?

A

substance at a temp. and pressure above its critical point and density near its liquid density
- have properties between those of gas and liquid

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40
Q

What is a solution?

A

homogenous mixture of two or more substances
- solution = solvent + solute

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41
Q

What is a solvent?

A

the component present in high concentration
- water is solvent —> aqueous solution

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42
Q

What is a solute?

A

the component present in low concentration

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43
Q

Strong Electrolytes

A
  • Substance Dissociation = completely
  • conductivity = high
  • ex. strong acids, strong bases, soluble ionic compounds
44
Q

Weak Electrolytes

A
  • Substance Dissociation = partially
  • Conductivity = low
  • ex. weak acids, weak bases
45
Q

Nonelectrolytes

A
  • Substance Dissociation = does not dissociate
  • Conductivity = no conductivity
  • ex. sugar, alcohols, organic compounds
46
Q

What is Solubility?

A

solubility of a solute in a particular solvent is the maximum concentration that may be achieved under given conditions when the dissolution process is at dynamic equilibrium
- concentration of dissolved solute remain constant
- amount of undissolved solute remain constant

47
Q

What is the solubility formula?

A

solubility = g solute needed to make saturated solution / 100 g solvent

48
Q

What is a saturated solution?

A

Maximum concentration of solute possible for a given temp. and pressure
- a solution containing solute that is equal to solubility
- additional solute will NOT dissolve

49
Q

What is an unsaturated solution?

A

A solution containing less solute than the equilibrium amount
- additional solute will dissolve

50
Q

What is a supersaturated solution?

A

A solution containing more solute than the equilibrium amount
- unstable
- a non-equilibrium state

51
Q

What are immiscible liquids?

A

Two mutually insoluble liquids
- get two separate phases

52
Q

What are miscible liquids?

A

Two liquids that dissolve in one another in all proportions
- get single phase
- form homogeneous solution

53
Q

What is the rule for formation of homogenous solutions?

A

“like dissolves like”
- polar solvents dissolve polar solute
- nonpolar solvents dissolve nonpolar substances

54
Q

What is the effect of temp on solid solubility?

A

For most solids, the silubility in water increases with increasing temp.

55
Q

What is the effect of temp on gas solubility?

A

The solubility of the gas in water decreases with increasing temp

56
Q

What is the effect of Pressure on gas solubility?

A

The higher the partial pressure of a gas above a liquid is, the more soluble the gas in the liquid is
- low pressure gas solubility is low
- high pressure gas solubility is high

57
Q

Factors Affecting Solubility - solid

A
  • temp increases —> solubility increases
  • pressure increases —> no effect
58
Q

Factors Affecting Solubility - gas

A
  • Temp increases —> solubility decreases
  • Pressure increases —> solubility increases
59
Q

Molarity (M) formula?

A

moles of solute / Liters of solution

60
Q

Molality (m) formula?

A

moles of solute / kilograms of solvent

61
Q

Mole Fraction (x) formula?

A

moles of solute / (mole of solute + moles of solvent)

62
Q

What is a Colligative Property?

A
  • Property of a solution
  • Depends only on the concentration of the solute
  • Do no depend on the chemical identity of the solute
63
Q

What are the colligative properties that we will discuss?

A
  • vapor pressure lowering
  • boiling point elevation
  • freezing point depression
  • osmotic pressure
64
Q

Colligative Properties - Nonelectryolyte

A

Substance that does not dissociate into ions when dissolved in water

65
Q

Colligative Properties - Electrolyte

A

Substance that dissociates into ions when dissolved in water

66
Q

What is Van’t Hoff Factor and what is it for electrolytes and nonelectrolytes?

A

i = moles particles in solution / moles of formula units dissolved
- for nonelectrolyte (molecular compounds) i = 1
- for electrolytes (soluble ionic compounds, acids) i > 1

67
Q

What does vapor pressure lowering mean?

A

The vapor pressure of the solution of nonvolatile solutes is lower than the vapor pressure of the pure solvent

68
Q

What are nonvolatile solutes?

A

solutes that cannot evaporate from solution

69
Q

What is Raoult’s Law?

A

quantifies the vapor pressure of a solution

70
Q

What are Raoult’s law for volatile components?

A
  • if both solvent and solute are volatile, they both contribute to the overall vapor pressure of solution
    Psolution=Psolvent+Psolute
  • the total vapor pressure of solution containing i volatile component is:
    Psolution=PA+PB+PC…
  • vapor pressure of each component is given by Raoults law:
    Psolution=XAPOA+XBPOB+XCPOC…
71
Q

What is boiling point elevation, ∆Tb?

A

elevation of the boiling point of a liquid by addition of a solute
- ∆Tb = BPsolution - BPpure solvent

72
Q

What is freezing point depression, ∆Tf ?

A

lowering of the freezing point of a liquid by addition of a solute
- ∆Tf = FPpure solvent - FPsolution

73
Q

Boiling Point Elevation?

A

Boiling point of a solution always higher than pure solvent
- BPsolution = BPpure solvent + ∆Tb

74
Q

Freezing Point Depression?

A

freezing point of solution always lower than pure solvent
- FPsolution = FPpure solvent - ∆Tf

75
Q

What is osmotic pressure?

A

the opposing pressure required to prevent the movement of solvent molecules through a semipermeable membrane
- TT = iMRT

76
Q

What is chemical kinetics?

A

The study of reaction rates (speeds)
- some chemical reactions are fast and some are slow

77
Q

What are chemical reaction rates?

A

The change in the amount of a reactance or product per unit of time

78
Q

Concentrations as a function of time

A
  • Concentration of reactant decreases with time
  • Concentration of product increases with time
79
Q

Rate Expressions

A
  • negative sign (-) for reactants
  • positive sign (+) for products
80
Q

What are measuring rates?

A

-reaction rate changes during reaction—>not constant
- often initially fast when lots of reactant present
- slower and slower as reactants are depleted
- Measured by average rate, instantaneous rate, and initial rate

81
Q

What are factors affecting reaction rates?

A
  1. chemical nature of reacting substances
  2. physical states of reactants
  3. temp of reactants
  4. concentrations of reactants
  5. presence of a catalyst
82
Q

What does the chemical nature of the reacting substances mean?

A

the rate of a reaction depends on the nature of the participating substances
- ex. calcium reacts moderately with water while potassium reacts quickly with water

83
Q

What does the physical states of reactants mean?

A

Reactants must contact in order to react. Therefore, reactions happen in liquid solution or gas phase
- Homogeneous solution: all reactants in same phase –> occurs rapidly
- Heterogeneous reaction: reactants in diff. phases. Only meet at interface. So, surface area determines reaction rate. Higher surface area = higher rate

84
Q

What does the temp. of reactants mean?

A

Chemical reactions typically occur faster at higher temps.
- ex. many chemical processes, reaction rates are approximately doubled when temp is raised by 10 degrees celcius

85
Q

What does concentrations of reactants mean?

A

Generally reaction rates usually increase when the concentration of one or more of reactants increases

86
Q

What does the presence of a catalyst mean?

A

Rate-accelerating agents
- ex. enzymes

87
Q

What are rate laws?

A

Mathematical expressions that describe the relationship between the rate and the concentration of its reactants

88
Q

What is rate law and order of reaction?

A

Exponents specify the order of reaction with respect to each reactant

89
Q

How do you find the overall order of reaction?

A

sum of order of each reactant in the rate law
- m+n

90
Q

What is the relationship between the order of a reaction and the changes in concentration and rate?

A
  • Zero order reaction: nothing changes
  • First order reaction: when [A] doubles = rate is double. When [A] triples = rate is triple. When [A] quadruple = rate is 4 times
    -Second order reaction: When [A] doubles = rate is 4 times. When [A] triples = rate is 9 times. When [A] quadruple = rate is 16 times
91
Q

What does concentration and time do?

A

Rate law tells us how rate of reaction varies with concentration

92
Q

How do we determine reaction order using graphs?

A
  • if [A] vs time is linear then reaction order is zero
  • if ln[A] vs time plot is linear, then reaction order is one
  • if 1/[A] vs time plot is linear then reaction order is 2
93
Q

What is the half-life of a reaction?

A

the time required for one-half of a given amount of reactant to be consumed
- half-life of the reaction depends on the order of reaction

94
Q

What does half-life show?

A

Shows inverse relation between the half-life, t1/2 and rate constant k
- faster reactions exhibit larger rate constants and shorter half-lives
- slower reactions exhibit smaller rate constants and longer half-lives

95
Q

What is the Collisions Theory?

A

model that emphasizes the energy and orientation of molecular collisions to explain and predict reaction kinetics

96
Q

What is the collisions theory based on?

A
  1. the rate of a reaction is proportional to rate of reactant collisions
  2. molecules must be oriented properly when they collide
  3. collisions must have minimum kinetic energy for successful reaction
97
Q

What is the collisions model?

A

-colliding molecules must have enough energy to cross the barrier
- energy barrier = activation energy, Ea

98
Q

What is activation energy?

A

the minimum energy necessary to form a product during a collision between reactants

99
Q

What is the Arrhenius equation?

A

mathematical relationship between the rate constant and the activation energy of a reaction
- k = Ae(-Ea/RT)
- A is related to frequency of collisions and the orientation of the reacting molecules
- e(-Ea/RT) is related to the fraction of collisions that has adequate energy to overcome the activation barrier

100
Q

What is a reaction intermediate?

A

a species that are produced in one step and consumed in a later step. Appear in mechanism but not in overall reaction.

101
Q

What is rate determining step?

A

step that occurs much more slowly than the other steps

102
Q

What needs to be met to validate a mechanism?

A
  1. elementary steps must sum to the overall reaction
  2. The rate law predicted by the mechanism (by slow step) must be consistent with the experimentally observed rate law
  3. each elementary step should have an order to three or less
103
Q

What is a catalyst?

A

substance that increases rate of chemical reaction but is not consumed by reaction

104
Q

What does adding a catalyst to a chemical reaction do?

A
  1. provide an alternative mechanism
  2. activation energy decreases
  3. rate constant increases
  4. reaction rate increases
105
Q

Where is catalyst found?

A

used up in early step and regenerated in later step

Spring 2024 (6 decks)

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