Energy diagrams Knowledge-Based Practice

Questions

1. 1.

   In a potential energy diagram for a chemical reaction, the activated complex has a potential energy of 180 kJ/mol, the forward activation energy is 75 kJ/mol, and the potential energy of the products is 45 kJ/mol. What is the enthalpy change ($\Delta H$) for this reaction?

   • A) +135 kJ/mol
   • B) +60 kJ/mol
   • C) -60 kJ/mol
   • D) -135 kJ/mol
2. 2.

   In a potential energy diagram for a chemical reaction, the reactants lie at a higher energy level than the products. Which statement correctly identifies the sign of the enthalpy change ($\Delta H$) and the relationship between the activation energies of the forward and reverse reactions?

   • A) $\Delta H < 0$, and the activation energy of the reverse reaction is greater than that of the forward reaction.
   • B) $\Delta H > 0$, and the activation energy of the forward reaction is greater than that of the reverse reaction.
   • C) $\Delta H < 0$, and the activation energy of the forward reaction is greater than that of the reverse reaction.
   • D) $\Delta H > 0$, and the activation energy of the reverse reaction is greater than that of the forward reaction.
3. 3.

   In a potential energy diagram for a two-step reaction mechanism, the initial reactants lie at 40 kJ/mol, the first transition state at 110 kJ/mol, the reaction intermediate at 80 kJ/mol, and the second transition state at 125 kJ/mol. What is the activation energy of the second elementary step?

   • A) 15 kJ/mol
   • B) 70 kJ/mol
   • C) 85 kJ/mol
   • D) 45 kJ/mol
4. 4.

   In an energy diagram for an uncatalyzed reaction, the potential energy of the reactants is 120 kJ/mol, the forward activation energy is 85 kJ/mol, and the reaction enthalpy change is +35 kJ/mol. If a catalyst is added that reduces the forward activation energy by 25 kJ/mol, what is the potential energy of the activated complex for the catalyzed pathway?

   • A) 180 kJ/mol
   • B) 145 kJ/mol
   • C) 205 kJ/mol
   • D) 155 kJ/mol
5. 5.

   In a potential energy diagram for a reversible chemical reaction, the reactants have an energy of 60 kJ/mol, the forward activation energy is 95 kJ/mol, and the reverse activation energy is 140 kJ/mol. What is the potential energy of the products?

   • A) 200 kJ/mol
   • B) 105 kJ/mol
   • C) 15 kJ/mol
   • D) -45 kJ/mol

Answers and step-by-step solutions appear after you finish the test.