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OCHEM > chapter 4 > Flashcards

chapter 4 Flashcards

1
Q

Thermodynamics: study of _______ changes that accompany chemical and physical transormations

A

energy

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2
Q

Kinetics: study of reaction _______

A

rates

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3
Q

a complete mechanism accounts for ______ reactancts used and _____ products formed

A

all
all

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4
Q

Radicals are _______ intermediates that have a(n) _______ number of electrons

A

reactive
odd

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5
Q

What are the 3 steps to a chain reaction mechanism?

A

1) initiation
2) propagation
3) termination

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6
Q

What is initiation composed of?

A

creating radicals using heat or light

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7
Q

What is propagation composed of?

A

radical + normal molecule
Two steps with the radical product from step 1 being the radical reactant in step 2

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8
Q

What is termination composed of?

A

radical + radical
mix the radicals together

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9
Q

Radical + radical reactions are _______

A

rare

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10
Q

While a chain reaction is in progress, the concentration of radicals is _______. The probability that two radicals will combine in a termination step is _______ than the probability that each radical will encounter a molecule of reactant and give a propagation step

A

low
lower

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11
Q

The termination step is more important at the _______ of the reaction when the free radicals are _______ likely to encounter another free radical. The chain reaction quickly stops

A

end
more

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12
Q

Keq (equilibrium constant) tells us the position of the equilibrium.
Keq>1 _______ reaction favored (______)
Keq<1 _______ reaction favored (______)

A

forward (products)
reverse (reactants)

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13
Q

Gibbs Free energy: change in _______ of a reaction. Can be calculated from Keq

A

free energy

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14
Q

A reaction with a _______ ΔG (_______) is favorable and spontaneous

A

negative (exergonic)

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15
Q

A reaction with a _______ ΔG (_______) is unfavorable because energy must be added to the system

A

positive (endergonic)

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16
Q

What are the 2 factors that contribute to change in free energy?

A

1) entropy (ΔS)
2) enthalpy (ΔH)

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17
Q

Entropy is the increase in the _______ of the system

A

disorder

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18
Q

Processes with an _______ in entropy are favored

A

increase (+ΔS)

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19
Q

Enthalpy is the heat _______ or _______ during a chemical reaction at standard conditions. All about bond _______!!!!!

A

released or absorbed
strength

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20
Q

An _______ reaction is the reaction when a weak bond is broken and a strong bond is formed

A

exothermic

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21
Q

_______ is the reaction when a strong bond is broken and a weak bond is formed

A

endothermic

22
Q

Bond strength is a measure of the heat change that occurs on breaking a bond, known as ________

A

bond dissociation energy

23
Q

What is the formula for enthalpy changes?

A

(BDE of bonds broken) - (BDE of bonds formed)

24
Q

Rate law works with the relationship between the concentrations of the _______ and the observed reaction rate. It can only be determined _______

A

reactants
experimentally

25
Q

Molecules must have enough _______ to get over an activation barrier (Ea)

A

energy

26
Q

formula for Overall order of reaction

A

add all orders

27
Q

The activation energy (Ea) represents the energy difference between the reactants and the _______

A

transition state

28
Q

In a reaction-energy diagram, the low points are _______, _______, and _______

A

reactants, intermediates, and products

29
Q

In a reaction-energy diagram, the high points are _______

A

transition states

30
Q

The rate-limiting step (r.d.s) is determined by the highest _______

A

activation energy (Ea)

31
Q

Hammond’s postulate: the structure of the _______ resembles the structure of the closest stable structure (reactants or products) in _______

A

transition state
energy

32
Q

Chlorination shows _______ radical selectivity. This is because of the preference for the primary radical and the secondary radical

A

poor

33
Q

a __° H is connected to a 1° carbon
a __° H is connected to a 2° carbon
a __° H is connected to a 3° carbon

A

1
2
3

34
Q

What is the term for a radical that is one away from an aromatic ring?

A

benzylic

35
Q

What is the term for a radical that is one away from a double bond?

A

allylic

36
Q

Bromination requires _______ conditions (hv and high temperature) compared to chlorination
- the reaction is _______

A

harsher
endothermic

37
Q

Why is bromination more selective than chlorination?

A

Hammond’s postulate (the transition state is closer in energy to the products), so the bond between H and Br is closer to happening

38
Q

Reactive intermediates are _______ species that react with another species as quickly as they are formed

A

short-lived

39
Q

What are the 3 types of reactive intermediates in order of their stability? (from least to most)

A

1) carbocation
2) radical
3) carbanion

40
Q

carbocation has __ nonbonding electrons and a _____ charge

A

0
positive

41
Q

Alkyl groups (-R) are _______, and they help stabilize an electron-deficient carbocation in 2 ways:

A

EDG’s
1) inductive
2) hyperconjugation

42
Q

Carbocation stability is _______ stable with more R groups
If they have the same amount of R groups then compare _______

A

more
resonance

43
Q

_______: overlap of filled orbitals on an adjacent alkyl group with the vacant p orbital of a cation

A

hyperconjugation

44
Q

Free radicals: ___ nonbonding electron(s), _______ charge

A

1
no

45
Q

radical stability depends on the _______ of the carbon then compare _______

A

degree
resonance

46
Q

Carbanions: ___ nonbonding electron(s), _____ charge

A

2
negative

47
Q

What are the 2 ways carbanions are stabilized by EWG’s?

A

1) inductive effect
2) resonance

48
Q

Carbanion stability is _______ stable with more R groups
If they have the same amount of R groups, then compare _______

A

less
resonance

49
Q

Carbenes: ___ nonbonding electrons, _______ charge
CH2 is called a _______ group

A

2
no
methylene

50
Q

What are the axis labels in an energy diagram? (2)

A

1) energy (y-axis)
2) reaction coordinate (x-axis)

OCHEM (9 decks)

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