1. Equilibrium And Rates Flashcards
What is the relationship between free energy change (ΔG) and the equilibrium constant (K)?
ΔG = -RT ln(K)
ΔG is the difference in free energy between the initial and final states.
What is the definition of the equilibrium constant K?
K = [products]/[reactants]
For the reaction involving methyl iodide and fluoride, K = [CH3F][I-]/[CH3I][F-].
What does a negative ΔG indicate about a reaction?
The reaction is exergonic (downhill) and favors the formation of products, meaning K > 1.
Most molecules in the reaction mixture will be products at equilibrium.
What is the significance of the Boltzmann distribution in relation to equilibrium?
It represents the distribution of molecules over two states based on energy levels.
If the final state has lower energy (ΔG < 0), the equilibrium lies to the right (more products).
What defines the transition state in a reaction?
The point of highest energy on the reaction coordinate.
It can be visualized as halfway between reactants and products with partially formed or broken bonds.
What is ΔG‡ in the context of chemical reactions?
The energy barrier or activation energy of the reaction.
It is the free energy required to reach the transition state from the initial state.
What is the rate equation for a bimolecular reaction A + B → products?
rate = k[A][B]
Where rate is in mol·L⁻¹·s⁻¹, [A] and [B] are concentrations, and k is the rate constant.
How is the rate constant k related to the energy barrier ΔG‡?
k ∝ exp(-ΔG‡/RT)
This indicates that the rate of reaction is sensitive to the height of the energy barrier.
Fill in the blank: The free energy change (ΔG) for a reaction is the difference in free energy between the _______ and _______.
initial and final states.
True or False: A reaction with K < 1 indicates that the reactants are favored at equilibrium.
True
What happens to the rate of reaction if the energy barrier (ΔG‡) increases?
The reaction slows down.
A larger barrier results in a slower reaction rate.
What is the relationship between the forward rate constant (k_forward) and the backward rate constant (k_backward) at equilibrium?
K = k_forward / k_backward
In the context of equilibrium, what does a higher concentration of products imply about the rate constants?
The backward rate constant (k_backward) must be smaller than the forward rate constant (k_forward).
What does the principle of microscopic reversibility state?
Reactions must have the same mechanism going forward or backwards.
What happens to the energy barrier for reaction as the exothermicity of a series of reactions increases?
The energy barrier for reaction will get smaller.
Describe the transition state of an exothermic reaction.
It will have an ‘early’, reactant-like TS.
What characterizes the transition state of an endothermic reaction?
It will have a ‘late’, product-like TS.
According to Hammond’s postulate, how does the energy content of two states affect their interconversion?
If they occur consecutively and have nearly the same energy content, their interconversion will involve only a small reorganization of molecular structure.
What can be inferred about the transition state from the structure of a stable molecule?
One can predict the effect of a substituent on a transition state by knowing its effect on a stable molecule.
Draw the mechanism and reaction coordinate for the addition of a Grignard reagent to a ketone?
This implies the reaction coordinate is reciprocal to the R-C-O distance.
In the enolisation of a ketone, what does Hammond’s postulate imply about the transition state? Draw the mechanism and reaction coordinate.
Structurally similar to the enol
The C-H bond and C-O bond are mostly broken, while the O-H bond and C=C bond are mostly formed.
What is the significance of the free energy diagram in acid-catalyzed enolization?
It illustrates the changes in bond formation and breaking during the reaction
The reaction coordinate is the C….H distance.
What is the process exemplified by the nitration of benzene? Draw the mechanism, with transition states and the reaction coordinate.
Electrophilic aromatic substitution
The nitronium ion attacks the π-electron cloud of benzene.
Why is methoxybenzene (anisole) nitrated faster than benzene?
The methoxy group stabilizes the cationic intermediates
This stabilization lowers the energy barrier for ortho and para attack.
What types of nitro compounds are formed when methoxybenzene is nitrated?
Ortho and para nitro compounds
No meta substituted product is formed.
What is the definition of kinetic control in chemical reactions?
Kinetic control refers to the situation where the product formed is the one that is produced the fastest, typically in irreversible reactions.
What characterizes a reaction that is under thermodynamic control?
In thermodynamic control, the major product formed is the most stable one, regardless of the barrier heights, and requires sufficient thermal energy for reversibility.
Indicate the mechanism and reaction coordinate for the reversible electrophilic substitution of 2-sulphonic acid to 1-sulphonic acid.
Indicate the curly arrows, type of reaction and reaction coordinate of the following:
The reaction conditions can influence whether a reaction yields kinetic or thermodynamic products.
Fill in the blank: The major product in thermodynamic control is the _______.
[most stable product]
Indicate what principle is being shown and the reaction coordinate of the following:
