chapter 4 Flashcards
Thermodynamics: study of _______ changes that accompany chemical and physical transormations
energy
Kinetics: study of reaction _______
rates
a complete mechanism accounts for ______ reactancts used and _____ products formed
all
all
Radicals are _______ intermediates that have a(n) _______ number of electrons
reactive
odd
What are the 3 steps to a chain reaction mechanism?
1) initiation
2) propagation
3) termination
What is initiation composed of?
creating radicals using heat or light
What is propagation composed of?
radical + normal molecule
Two steps with the radical product from step 1 being the radical reactant in step 2
What is termination composed of?
radical + radical
mix the radicals together
Radical + radical reactions are _______
rare
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
low
lower
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
end
more
Keq (equilibrium constant) tells us the position of the equilibrium.
Keq>1 _______ reaction favored (______)
Keq<1 _______ reaction favored (______)
forward (products)
reverse (reactants)
Gibbs Free energy: change in _______ of a reaction. Can be calculated from Keq
free energy
A reaction with a _______ ΔG (_______) is favorable and spontaneous
negative (exergonic)
A reaction with a _______ ΔG (_______) is unfavorable because energy must be added to the system
positive (endergonic)
What are the 2 factors that contribute to change in free energy?
1) entropy (ΔS)
2) enthalpy (ΔH)
Entropy is the increase in the _______ of the system
disorder
Processes with an _______ in entropy are favored
increase (+ΔS)
Enthalpy is the heat _______ or _______ during a chemical reaction at standard conditions. All about bond _______!!!!!
released or absorbed
strength
An _______ reaction is the reaction when a weak bond is broken and a strong bond is formed
exothermic
_______ is the reaction when a strong bond is broken and a weak bond is formed
endothermic
Bond strength is a measure of the heat change that occurs on breaking a bond, known as ________
bond dissociation energy
What is the formula for enthalpy changes?
(BDE of bonds broken) - (BDE of bonds formed)
Rate law works with the relationship between the concentrations of the _______ and the observed reaction rate. It can only be determined _______
reactants
experimentally
Molecules must have enough _______ to get over an activation barrier (Ea)
energy
formula for Overall order of reaction
add all orders
The activation energy (Ea) represents the energy difference between the reactants and the _______
transition state
In a reaction-energy diagram, the low points are _______, _______, and _______
reactants, intermediates, and products
In a reaction-energy diagram, the high points are _______
transition states
The rate-limiting step (r.d.s) is determined by the highest _______
activation energy (Ea)
Hammond’s postulate: the structure of the _______ resembles the structure of the closest stable structure (reactants or products) in _______
transition state
energy
Chlorination shows _______ radical selectivity. This is because of the preference for the primary radical and the secondary radical
poor
a __° H is connected to a 1° carbon
a __° H is connected to a 2° carbon
a __° H is connected to a 3° carbon
1
2
3
What is the term for a radical that is one away from an aromatic ring?
benzylic
What is the term for a radical that is one away from a double bond?
allylic
Bromination requires _______ conditions (hv and high temperature) compared to chlorination
- the reaction is _______
harsher
endothermic
Why is bromination more selective than chlorination?
Hammond’s postulate (the transition state is closer in energy to the products), so the bond between H and Br is closer to happening
Reactive intermediates are _______ species that react with another species as quickly as they are formed
short-lived
What are the 3 types of reactive intermediates in order of their stability? (from least to most)
1) carbocation
2) radical
3) carbanion
carbocation has __ nonbonding electrons and a _____ charge
0
positive
Alkyl groups (-R) are _______, and they help stabilize an electron-deficient carbocation in 2 ways:
EDG’s
1) inductive
2) hyperconjugation
Carbocation stability is _______ stable with more R groups
If they have the same amount of R groups then compare _______
more
resonance
_______: overlap of filled orbitals on an adjacent alkyl group with the vacant p orbital of a cation
hyperconjugation
Free radicals: ___ nonbonding electron(s), _______ charge
1
no
radical stability depends on the _______ of the carbon then compare _______
degree
resonance
Carbanions: ___ nonbonding electron(s), _____ charge
2
negative
What are the 2 ways carbanions are stabilized by EWG’s?
1) inductive effect
2) resonance
Carbanion stability is _______ stable with more R groups
If they have the same amount of R groups, then compare _______
less
resonance
Carbenes: ___ nonbonding electrons, _______ charge
CH2 is called a _______ group
2
no
methylene
What are the axis labels in an energy diagram? (2)
1) energy (y-axis)
2) reaction coordinate (x-axis)
