AP Chemistry · Topic 5.6
Reaction Energy Profile Practice
Part of Kinetics.(TRA-4.C)
Practice questions
12
Sample questions
5 of 12 — sign in to practice the rest with adaptive difficulty and mastery tracking.
Sample 1difficulty 1/5
The marked point at the peak of the energy profile represents the:
- A
Final product
- Bcheck_circle
Transition state (activated complex)
- C
Intermediate
- D
Catalyst
Why
The peak corresponds to the highest-energy structure along the reaction path: the transition state.
- A
Sample 2difficulty 2/5
A reaction-energy diagram with two transition states (peaks) is shown.
Which step is rate determining?
- A
The second step (TS2).
- Bcheck_circle
The first step (TS1, higher peak).
- C
Whichever has lower Eₐ.
- D
The exothermic step.
Why
The slow (rate-determining) step is the one with the highest activation barrier. Here TS1 is taller, so step 1 is rate-determining.
- A
Sample 3difficulty 2/5
The energy profile of a one-step reaction is shown.
On the energy profile diagram, the activation energy Ea is best described as:
- A
Total energy of products
- B
Difference between reactants and products
- Ccheck_circle
Energy from reactants to transition state peak
- D
Energy from products to peak
Why
Ea is the energy required to reach the transition state from reactants.
- A
Sample 4difficulty 2/5
An energy profile shows products at lower energy than reactants.
The reaction depicted is:
- A
Reversible only above 0 K
- B
Thermoneutral
- Ccheck_circle
Exothermic (products lower than reactants)
- D
Endothermic
Why
Products are lower in energy than reactants, indicating heat is released — exothermic.
- A
Sample 5difficulty 2/5
On the diagram, Ea(fwd) = 140 kJ/mol and Ea(rev) = 80 kJ/mol.
What is ΔH for the forward reaction?
- A
-220 kJ/mol
- B
-60 kJ/mol
- Ccheck_circle
+60 kJ/mol
- D
+220 kJ/mol
Why
ΔH = Ea(fwd) - Ea(rev) = 140 - 80 = +60 kJ/mol (endothermic).
- A