Activation energy Knowledge-Based Download PDF

Questions

1. 1.

   In an exergonic chemical reaction, how does the activation energy of the reverse reaction compare to the activation energy of the forward reaction?

   • A) It is equal to the forward activation energy because both directions pass through the same transition state.
   • B) It is lower than the forward activation energy because the products reside at a more stable energy level.
   • C) It is greater than the forward activation energy by an amount equal to the absolute value of the net free energy change.
   • D) It is zero because exergonic reactions release free energy and cannot proceed in the reverse direction.
2. 2.

   Which of the following describes a specific mechanism by which an enzyme lowers the activation energy of a chemical reaction?

   • A) Transferring metabolic heat directly to the substrate to increase its kinetic energy
   • B) Increasing the net free energy difference between the initial reactants and the products
   • C) Changing an endergonic pathway into an exergonic pathway by shifting reaction equilibrium
   • D) Straining critical chemical bonds in the substrate to facilitate their breakage
3. 3.

   Why does an exergonic reaction with a high activation energy proceed very slowly at physiological temperatures?

   • A) Only a small fraction of reactant molecules possess enough kinetic energy to overcome the barrier.
   • B) The reaction has a positive change in free energy ($\Delta G > 0$) that prevents it from releasing energy.
   • C) Enzymes permanently alter the chemical equilibrium of the reaction to favor the reactants.
   • D) The products are less stable than the reactants, requiring continuous external heat input.
4. 4.

   What molecular condition must reactant molecules reach by absorbing activation energy before a chemical reaction can proceed to form products?

   • A) An unstable transition state in which chemical bonds are strained and ready to break
   • B) A lower-energy ground state in which molecules achieve maximum thermodynamic stability
   • C) A dynamic equilibrium state in which forward and reverse reaction rates become equal
   • D) An irreversibly denatured state in which secondary protein structures unravel completely
5. 5.

   Which statement correctly describes the effect of an enzyme on the activation energy and overall free energy change ($\Delta G$) of a chemical reaction?

   • A) An enzyme increases the activation energy and makes the overall $\Delta G$ more negative.
   • B) An enzyme lowers the activation energy and decreases the overall $\Delta G$ of the reaction.
   • C) An enzyme lowers the activation energy while leaving the overall $\Delta G$ unchanged.
   • D) An enzyme does not affect the activation energy but increases the overall $\Delta G$.