Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

CHEM333 (RBL) > 1. Equilibrium And Rates > Flashcards

1. Equilibrium And Rates Flashcards

1
Q

What does the x-axis represent in a free energy diagram for a bimolecular reaction?

A

The reaction coordinate, which is some measure of the extent of reaction.

In this case, it might be the C-I bond distance.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the relationship between free energy change (ΔG) and the equilibrium constant (K)?

A

ΔG = -RT ln(K)

ΔG is the difference in free energy between the initial and final states.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the definition of the equilibrium constant K?

A

K = [products]/[reactants]

For the reaction involving methyl iodide and fluoride, K = [CH3F][I-]/[CH3I][F-].

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does a negative ΔG indicate about a reaction?

A

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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the significance of the Boltzmann distribution in relation to equilibrium?

A

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).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What defines the transition state in a reaction?

A

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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is ΔG‡ in the context of chemical reactions?

A

The energy barrier or activation energy of the reaction.

It is the free energy required to reach the transition state from the initial state.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the rate equation for a bimolecular reaction A + B → products?

A

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 well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How is the rate constant k related to the energy barrier ΔG‡?

A

k ∝ exp(-ΔG‡/RT)

This indicates that the rate of reaction is sensitive to the height of the energy barrier.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Fill in the blank: The free energy change (ΔG) for a reaction is the difference in free energy between the _______ and _______.

A

initial and final states.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

True or False: A reaction with K < 1 indicates that the reactants are favored at equilibrium.

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What happens to the rate of reaction if the energy barrier (ΔG‡) increases?

A

The reaction slows down.

A larger barrier results in a slower reaction rate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What does a K value of 100 indicate regarding the percent of products at equilibrium?

A

99% product at equilibrium.

Corresponds to a ΔG of -11.4 kJ/mol.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What occurs at equilibrium in a chemical reaction?

A

The reactants turn into products as fast as the products turn back into reactants.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the relationship between the forward rate constant (k_forward) and the backward rate constant (k_backward) at equilibrium?

A

K = k_forward / k_backward

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

True or False: At equilibrium, the rates of the forward and backward reactions are different.

A

False

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

In the context of equilibrium, what does a higher concentration of products imply about the rate constants?

A

The backward rate constant (k_backward) must be smaller than the forward rate constant (k_forward).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What does the principle of microscopic reversibility state?

A

Reactions must have the same mechanism going forward or backwards.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What does the transition state (TS) represent in a chemical reaction?

A

The point along the reaction coordinate where reactants and products intersect in energy.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Fill in the blank: The energy of the transition state will be lower than the intersection point because a bond is being made at the same time as one is being _______.

A

broken

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What happens to the energy barrier for reaction as the exothermicity of a series of reactions increases?

A

The energy barrier for reaction will get smaller.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Describe the transition state of an exothermic reaction.

A

It will have an ‘early’, reactant-like TS.

23
Q

What characterizes the transition state of an endothermic reaction?

A

It will have a ‘late’, product-like TS.

24
Q

According to Hammond’s postulate, how does the energy content of two states affect their interconversion?

A

If they occur consecutively and have nearly the same energy content, their interconversion will involve only a small reorganization of molecular structure.

25
Q

What is the significance of molecules with similar energy content in terms of their structure?

A

Molecules with similar energy tend to resemble each other.

26
Q

What is the relationship between the energy of the transition state and the energy of reactants and products?

A

The energy of the TS will be lower than the intersection point.

27
Q

What can be inferred about the transition state from the structure of a stable molecule?

A

One can predict the effect of a substituent on a transition state by knowing its effect on a stable molecule.

28
Q

What type of reaction occurs when a Grignard reagent is added to a ketone?

A

Exothermic reaction

Driven by the strong 0-MgX bond in the product.

29
Q

According to Hammond’s postulate, what will the transition state (TS) look like in the addition of a Grignard reagent to a ketone?

A

More like the starting ketone than the product alkoxide

This implies the reaction coordinate is reciprocal to the R-C-O distance.

30
Q

What is the thermodynamic nature of the enolisation of a ketone?

A

Endothermic reaction

It is uphill thermodynamically.

31
Q

In the enolisation of a ketone, what does Hammond’s postulate imply about the transition state?

A

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.

32
Q

What is the significance of the free energy diagram in acid-catalyzed enolization?

A

It illustrates the changes in bond formation and breaking during the reaction

The reaction coordinate is the C….H distance.

33
Q

What is the process exemplified by the nitration of benzene?

A

Electrophilic aromatic substitution

The nitronium ion attacks the π-electron cloud of benzene.

34
Q

What type of intermediate is formed during the nitration of benzene?

A

Cationic intermediate

This intermediate is represented by a dip in the free energy curve.

35
Q

What does Hammond’s postulate state about the first transition state in the nitration of benzene?

A

It will look more like the intermediate than like benzene

This is due to the energy proximity to the intermediate.

36
Q

How do substituents that interact with a positive charge affect the reaction rate in electrophilic aromatic substitution?

A

They have a bigger effect on the energy of the transition state than on benzene

This accounts for rates and regioselectivities.

37
Q

Why is methoxybenzene (anisole) nitrated faster than benzene?

A

The methoxy group stabilizes the cationic intermediates

This stabilization lowers the energy barrier for ortho and para attack.

38
Q

What types of nitro compounds are formed when methoxybenzene is nitrated?

A

Ortho and para nitro compounds

No meta substituted product is formed.

39
Q

What does the transition state look like when the proton falls off the intermediate in the nitration of benzene?

A

More like the intermediate than the product

This is because it is closer to it in energy.

40
Q

What is the definition of kinetic control in chemical reactions?

A

Kinetic control refers to the situation where the product formed is the one that is produced the fastest, typically in irreversible reactions.

41
Q

What characterizes a reaction that is under thermodynamic control?

A

In thermodynamic control, the major product formed is the most stable one, regardless of the barrier heights, and requires sufficient thermal energy for reversibility.

42
Q

In a scenario with two competing reactions A → B and A → C, what determines the ratio of concentrations of B and C?

A

The ratio of concentrations of B and C is determined by the ratio of rate constants, expressed as:
* Rate of formation of B
* Rate of formation of C

43
Q

Fill in the blank: The selectivity of a reaction depends only on the difference in _______.

A

[free energy barriers]

44
Q

How can selectivity be increased in a reaction at low temperatures?

A

Running the reaction at low temperatures allows more molecules to overcome the smaller energy barrier leading to the desired product.

45
Q

True or False: At low temperatures, the overall rate of the reaction will increase.

A

False

46
Q

What is the role of thermal energy in reversible reactions?

A

Thermal energy allows for back reactions to occur, making the system reach equilibrium.

47
Q

What is the relationship between concentrations of products B and C at equilibrium?

A

The concentrations of B and C are related by an effective equilibrium constant, expressed as:
* [B][C] = K_eq = exp(-ΔG/RT)

48
Q

Provide an example of a reaction that can give either kinetic or thermodynamic products.

A

Deprotonation of an unsymmetrical ketone can yield either the kinetic or the thermodynamic enolate depending on the base used.

49
Q

What happens to the product distribution of naphthalene sulphonation at different temperatures?

A

At 80 °C, 100% of the product is 1-sulphonic acid, while at 160 °C, the product distribution is 20% 1-sulphonic acid and 80% 2-sulphonic acid.

50
Q

What does the reaction condition affect in terms of product formation?

A

The reaction conditions can influence whether a reaction yields kinetic or thermodynamic products.

51
Q

In the context of the reactions A → B and A → C, which product is favored under kinetic control?

A

Product B is favored under kinetic control due to a smaller energy barrier.

52
Q

What happens to stability when comparing products B and C under kinetic control?

A

Product B is less stable than product C under kinetic control.

53
Q

Fill in the blank: The major product in thermodynamic control is the _______.

A

[most stable product]

54
Q

What impact does increasing temperature have on reversible reactions?

A

Increasing temperature can help overcome energy barriers, facilitating back reactions and achieving equilibrium.

CHEM333 (RBL) (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions