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Ochem > chapter 4 > Flashcards

chapter 4 Flashcards

1
Q

thermodynamics

A

deals with energy changes accompanying chemical and physical transformations
- describes properties of systems at equilibrium

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2
Q

kinetics

A

variation of reaction rates with different condition and concentrations of reagents
- rates: how fast something happens

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3
Q

3 steps of chain reaction mechanism

A
  1. initiation
  2. propagation
  3. termination
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4
Q

initiation

A

generates reactive intermediate

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5
Q

propagation

A

reactive intermediate reacts with stable molecule to form product and another reactive intermediate

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6
Q

termination

A

reactive intermediates destroyed

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7
Q

what kind of light is used to split Cl2

A

blue light (hv)

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8
Q

reactive intermediate

A

short-lived series never present in high concentration because it reacts as quickly as it is formed

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9
Q

free radicals

A

species with unpaired electrons

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10
Q

stability of free radicals

A

methyl < primary < secondary < tertiary < allylic/benzylic

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11
Q

stability of free radicals according to hybridization

A

sp < sp2 < sp3

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12
Q

if Keq is larger than 1…

A

then reaction is favored from left to right

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13
Q

if Keq is less than 1

A

reaction is favored from right to left

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14
Q

Gibbs free energy (delta G)

A

change in free energy:
(free energy of products) - (free energy of reactants)

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15
Q

delta H (enthalpy)

A

(enthalpy of products) - (enthalpy of reactants)

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16
Q

delta G in relation to H,T,S

A

delta G = delta H - T(delta S)

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17
Q

delta S (entropy)

A

(entropy of products) - (entropy of reactants)

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18
Q

reactions tend to favor products with the ________ enthalpy

A

lowest

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19
Q

change in enthalpy (heat of reaction)

A

amount of heat evolved or consumed in the course of a reaction

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20
Q

do exergonic reactions have a negative or positive g

A

negative

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21
Q

do endergonic reactions have a negative or positive g

A

positive

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22
Q

if weaker bonds are broken and stronger bonds are formed, it is an ____________ reaction

A

exothermic

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23
Q

if stronger bonds are broken and weaker bonds are formed, it is an ____________ reaction

A

endothermic

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24
Q

entropy

A

measure of randomness, disorder, or freedom of motion

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25
Q

reactions favor products with the _________ entropy

A

greatest

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26
Q

bond-dissociation enthalpy (BDE)

A

amount of enthalpy required to break a particular bond homolytically

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27
Q

homolytic cleavage

A

each bonded atom retains one of bond’s two electrons - free radicals result

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28
Q

heterolytic cleavage

A

one of the atoms retains both electrons - ions results

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29
Q

is energy consumed or released when bonds are formed

30
Q

is energy consumed or released when bonds are broken

31
Q

are bond-dissociation enthalpies positive or negative

A

positive (endothermic)

32
Q

what is the rate of reaction a measure of

A

how fast the products appear and the reactants disappear

33
Q

reaction rates depend on the concentration of the __________

34
Q

the values of the powers in a rate equation are determined _____________

A

experimentally

35
Q

activation energy

A

energy difference between the reactants and the transition state

36
Q

transition state

A

highest-energy state in a molecular collision that leads to reaction

37
Q

is a transition state stable or unstable

38
Q

is a transition state an intermediate

39
Q

is the Ea value always positive or negative

40
Q

catalysts

A

lower the activation energy and increase the reaction rate, but don’t affect energies of reactants/products

41
Q

enzymes

A

biological catalysts

42
Q

which step determines the rate of a reaction

A

the highest-energy step (transition state)

43
Q

does temperature usually increase or decrease reaction rate

A

increase - within limits

44
Q

is the transition state of an endothermic reaction closer to the reactants or products

45
Q

is the transition state of an exothermic reaction closer to the reactants or products

46
Q

is chlorination more or less selective

47
Q

is bromination more or less selective

48
Q

is chlorination exothermic or endothermic

A

exothermic

49
Q

is bromination exothermic or endothermic

A

endothermic

50
Q

rate-limiting step of bromination and chlorination

A

first propagation step

51
Q

Hammond’s postulate

A

related species that are closer in energy are closer in structure

52
Q

is there a large or small difference in Ea of bromination

53
Q

is there a large or small difference of Ea in chlorination

54
Q

radical inhibitors

A

slow down or prevent free-radical reactions

55
Q

carbocation

A

species that contains a C atom bearing a positive charge

56
Q

2 ways an alkyl group stabilizes a carbocation

A
  1. inductive effect
  2. partial overlap of filled orbitals with empty ones
57
Q

4 types of reactive intermediates

A
  1. carbocation
  2. radical
  3. carbanion
  4. carbene
58
Q

stability of carbocations

A

resonance > 3 > 2 > 1 > methyl

59
Q

hybridization of carbocations

60
Q

hybridization of free radicals

61
Q

stability of radicals

A

resonance > 3 > 2 > 1 > methyl

62
Q

carbanion

A

has trivalent carbon atom that bears a negative charge
- Lewis base)

63
Q

hybridization of carbanion

64
Q

stability of carbanions

A

resonance > methyl > 1 > 2 > 3

65
Q

carbenes

A

uncharged reactive intermediates containing a divalent carbon atom

66
Q

hybridization of carbene

67
Q

what happens when 2 carbenes collide

A

make alkene (double bond)

68
Q

properties of carbocations

A

electrophilic, strong acids

69
Q

properties of radicals

A

electron-deficient

70
Q

properties of carbanions

A

nucleophilic, strong bases

71
Q

properties of carbenes

A

both nucleophilic and electrophilic

Ochem (22 decks)

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