Question

which statement best describes how an enzyme affects the activation energy of a chemical reaction?
interactions between reactants and specific r - groups in the enzyme stabilize the transition state, which reduces activation energy.
when reactants bind to the active site, the enzyme changes shape, which increases activation energy.
the enzyme adds thermal energy to chemical reactions when binding to reactants, which reduces activation energy.
the free energy of the reaction is increased when reactants bind to the active site, which increases activation energy.

Explanation:

Enzymes are biological catalysts. Catalysts work by stabilizing the transition state of a reaction. The transition state is the high - energy intermediate in a chemical reaction. By stabilizing it (through interactions between reactants and specific groups in the enzyme, like R - groups in amino acids of the enzyme), the energy barrier (activation energy) for the reaction is lowered.

• Option 2: Enzymes lower activation energy, not increase it. When reactants bind to the active site (induced fit model), the enzyme changes shape to better fit the reactants, which helps in stabilizing the transition state (lowering activation energy).
• Option 3: Enzymes do not add thermal energy. Thermal energy is related to the temperature of the system. Enzymes work by a mechanism of binding and stabilizing the transition state.
• Option 4: The free energy of the reaction (\(\Delta G\)) is a property of the reaction itself (\(\Delta G=\Delta H - T\Delta S\), where \(\Delta H\) is enthalpy change, \(T\) is temperature, and \(\Delta S\) is entropy change). Enzymes do not change \(\Delta G\) of the reaction. They only lower the activation energy (\(E_{a}\)) which is the energy required to reach the transition state.

Answer:

Interactions between reactants and specific R - groups in the enzyme stabilize the transition state, which reduces activation energy.