Energy Diagram Practice Problems
The bromination of ethane (CH3CH3) consists of three steps.
1. Br2 → 2 Br•
ΔH° = +190 kJ/mol
Ea = 190 kJ/mol
2. CH3CH3 + Br• —> •CH2CH3 + HBr
ΔH° = +57 kJ/mol
Ea = 79 kJ/mol
3. •CH2CH3 + Br2 —> CH3CH2Br + Br•
ΔH° = −113 kJ/mol
Ea = 4 kJ/mol
Write a reaction-energy diagram that corresponds to the bromination of X. Make sure you label the rate-limiting step in the diagram.
There are two possible pathways for ionic addition of HBr to 1-ethylcyclohexene. Draw an approximate reaction-energy diagram showing the curves for these pathways.
(a) Formation of 1-bromo-1-ethylcyclohexane (major product)
(b) Formation of 1-bromo-2-ethylcyclohexane (minor product)
Point out how these curves show that the major product 1-bromo-1-ethylcyclohexane should be formed faster than the minor product 1-bromo-2-ethylcyclohexane.
Write a reaction-energy diagram that corresponds to a one-step exothermic reaction. Make sure that all parts of the diagram are labeled appropriately.
For the following transformation, provide an energy profile diagram, and label all the reactants, products, intermediates, and transition states.
Illustrate the energy profile diagram of a one-step reaction with a standard enthalpy change (ΔH°) of 0 kcal/mol and an activation energy (Ea) of 6 kcal/mol.
Consider the following energy profile diagram:
Which will occur at a faster rate: the forward reaction or the reverse reaction?
Provide an energy profile diagram for an exothermic one-step reaction and label the reactants, products, intermediates, transition states, activation energies (Ea), and ΔG°, if applicable.
Since ethylcyclopentan-1-ylium is more stable than 2-ethylcyclopentan-1-ylium, provide an energy profile diagram that shows ethylcyclopentan-1-ylium is formed faster than 2-ethylcyclopentan-1-ylium in the reaction below.
The following equation is used to calculate the bond angles in a regular polygon with n sides:
180° - 360°/n
Using the above equation, calculate the bond angles in a regular:
Consider the reaction diagram shown below.
a. Determine which step in the forward direction has the highest activation energy.
b. Is the second intermediate more likely to return to the first intermediate or to proceed to produce the product?
c. What step is the rate-determining step?
The reaction of
follows the reaction coordinate diagram shown below.
a. Count the number of intermediate and transition states present.
b. Arrange the reaction species in order of increasing stability.
c. Which is more stable, the transition state between X and Y, or the transition state between Y and Z?
d. Which step has a higher rate constant in the forward direction? In the reverse direction?
An alkyl halide is produced from the alkene shown below.
Draw a reaction coordinate diagram for the reaction, taking into account that the product is more stable than the reactant.
Which graph below illustrates the reaction coordinate diagram of monohydrobromination of (E)-2-methyl-1,3-hexadiene and monohydrobromination of 2-methyl-1,5-hexadiene?
It takes several steps to create product I from reactant A. The reaction proceeds as illustrated in the reaction coordinate diagram below.
a. How many intermediates are generated throughout the synthesis?
b. List the letters that correspond to the transition states.
c. Identify which step of the reaction is the fastest.
d. Between A and I, which one is more stable?
e. Does E or I form faster from G?
f. Which intermediate is the most stable?
Write an appropriate reaction-energy diagram that corresponds to the reaction between methyl radical and HBr shown below:
•CH3 + HBr —> CH4 + Br•
The following reaction has an overall ΔH° of −310. kJ/mol (−74.0 kcal/mol) and activation energy of 47.4 kJ/mol (11.3 kcal/mol).
•CH2CH3 + F2 → CH3CH2F + F•
Provide the equation for the reverse reaction, and determine its activation energy.