Energy diagrams Knowledge-Based Download PDF

Questions

1. 1.

   Which of the following modifications is observed in the potential energy diagram of a chemical reaction when a positive catalyst is added?

   • A) The enthalpy change of the reaction becomes more negative.
   • B) The potential energy level of the reactants increases.
   • C) The potential energy of the activated complex decreases.
   • D) The potential energy level of the products decreases.
2. 2.

   For an endothermic chemical reaction, which of the following quantities in its potential energy diagram must always be strictly greater than the enthalpy change ($\Delta H$) of the reaction?

   • A) The activation energy of the reverse reaction ($E_{\text{a, rev}}$)
   • B) The potential energy of the reactants
   • C) The activation energy of the forward reaction ($E_{\text{a, fwd}}$)
   • D) The potential energy of the products
3. 3.

   In the potential energy diagram of a reversible chemical reaction, the potential energy level of the reactants is higher than that of the products. Which of the following statements is correct for this reaction?

   • A) The reaction is exothermic in the forward direction, and the activation energy of the reverse reaction is greater than the activation energy of the forward reaction.
   • B) The reaction is endothermic in the forward direction, and the activation energy of the reverse reaction is greater than the activation energy of the forward reaction.
   • C) The reaction is exothermic in the forward direction, and the activation energy of the reverse reaction is less than the activation energy of the forward reaction.
   • D) The reaction is endothermic in the forward direction, and the activation energy of the reverse reaction is equal to the activation energy of the forward reaction.
4. 4.

   In a potential energy diagram for a chemical reaction, the potential energy of the reactants is 40 kJ/mol, the potential energy of the products is 95 kJ/mol, and the potential energy of the activated complex is 175 kJ/mol. What is the activation energy of the reverse reaction ($E_{\text{a, rev}}$)?

   • A) 55 kJ/mol
   • B) 135 kJ/mol
   • C) 80 kJ/mol
   • D) 270 kJ/mol
5. 5.

   In an energy diagram for a reversible reaction, the activation energy of the forward reaction is 50 kJ/mol and the activation energy of the reverse reaction is 90 kJ/mol. What is the enthalpy change ($\Delta H$) of the forward reaction, and how is the reaction classified thermochemically?

   • A) +40 kJ/mol; endothermic
   • B) -40 kJ/mol; exothermic
   • C) -140 kJ/mol; exothermic
   • D) +140 kJ/mol; endothermic