Bioenergetics and Biological Oxidation–Reduction (5E) - Chem & Physics

1. What happens to oxidation state when a species is oxidized?

   Oxidation state increases. Loss of electrons results in a higher (more positive) oxidation number for the oxidized atom.

2. Which type of reaction has $\Delta G < 0$ and is thermodynamically spontaneous?

   Exergonic reaction. Releases free energy, making the process favorable and able to occur without external input under standard conditions.

3. Which redox cofactor is the reduced form: $\text{NAD}^+$ or $\text{NADH}$?

   $\text{NADH}$. Carries electrons gained during metabolic reductions, serving as an electron donor in the electron transport chain.

4. State the relationship between $\Delta G^\circ$, $R$, $T$, and the equilibrium constant $K$.

   $\Delta G^\circ = -RT\ln K$. Links standard free energy to the equilibrium constant, indicating reaction favorability at equilibrium.

5. What is the condition for a spontaneous galvanic cell in terms of $E_{cell}$?

   $E_{cell} > 0$. Positive cell potential indicates a spontaneous redox reaction driving electron flow.

6. Identify the direction of electron flow in a galvanic cell: anode to cathode or cathode to anode?

   Anode to cathode. Electrons flow from the site of oxidation (anode) to the site of reduction (cathode) in spontaneous cells.

7. What happens to oxidation state when a species is reduced?

   Oxidation state decreases. Gain of electrons results in a lower (more negative) oxidation number for the reduced atom.

8. Which process directly uses an $\text{H}^+$ gradient to synthesize ATP from ADP and $\text{P}_i$?

   ATP synthase (chemiosmosis). Harnesses the proton motive force across the membrane to drive ATP production via oxidative phosphorylation.

9. State the relationship between $\Delta G$, $\Delta H$, $T$, and $\Delta S$.

   $\Delta G = \Delta H - T\Delta S$. This equation determines the spontaneity of a reaction by balancing enthalpy, temperature, and entropy changes.

10. Which electrode is the site of oxidation in any electrochemical cell?

    Anode. Oxidation, or loss of electrons, always occurs at this electrode in both galvanic and electrolytic cells.

11. What is the condition for equilibrium in terms of Gibbs free energy change?

    $\Delta G = 0$. At equilibrium, the system has no net change in free energy, so forward and reverse rates are equal.

12. Which redox cofactor is the reduced form: $\text{FAD}$ or $\text{FADH}_2$?

    $\text{FADH}_2$. Holds electrons from flavoprotein reductions, contributing to the proton gradient in mitochondrial respiration.

13. Identify the sign of $\Delta G^\circ$ when $K > 1$ for a reaction.

    $\Delta G^\circ < 0$. When $K > 1$, products are favored at equilibrium, corresponding to a spontaneous reaction under standard conditions.

14. State the relationship between $\Delta G$, $\Delta G^\circ$, $R$, $T$, and $Q$.

    $\Delta G = \Delta G^\circ + RT\ln Q$. This formula calculates free energy under non-standard conditions using the reaction quotient $Q$.

15. What is the definition of oxidation in terms of electron transfer?

    Loss of electrons. Involves the transfer of electrons from a species, increasing its oxidation state.

16. Which agent is oxidized in a redox reaction: oxidizing agent or reducing agent?

    Reducing agent. Donates electrons to another species, thereby undergoing oxidation itself in the process.

17. State the relationship between cell potential and free energy: $\Delta G$ and $E$.

    $\Delta G = -nFE$. Relates the free energy change to the cell potential $E$ and the number of electrons transferred $n$, with Faraday's constant $F$.

18. Which agent is reduced in a redox reaction: oxidizing agent or reducing agent?

    Oxidizing agent. Accepts electrons from another species, thereby undergoing reduction itself in the process.

19. For standard conditions, state the relationship between $E^\circ$, $n$, $F$, and $\Delta G^\circ$.

    $\Delta G^\circ = -nFE^\circ$. Under standard conditions, this equation connects electrochemical potential to thermodynamic spontaneity.

20. State the formula for standard cell potential using standard reduction potentials.

    $E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}$. Calculated by subtracting the anode's reduction potential from the cathode's to determine overall cell potential.

21. Which electrode is the site of reduction in any electrochemical cell?

    Cathode. Reduction, or gain of electrons, always occurs at this electrode in both galvanic and electrolytic cells.

22. What is the definition of reduction in terms of electron transfer?

    Gain of electrons. Involves the acceptance of electrons by a species, decreasing its oxidation state.

23. What is the sign of $\Delta G$ when $Q > K$ for a reaction at constant $T$?

    $\Delta G > 0$. Indicates the reaction proceeds in the reverse direction toward equilibrium when products exceed reactants.

24. Which type of reaction has $\Delta G > 0$ and requires energy input to proceed?

    Endergonic reaction. Absorbs free energy, rendering the reaction non-spontaneous and necessitating coupling to an exergonic process in biological systems.

25. What is the sign of $\Delta G$ when $Q < K$ for a reaction at constant $T$?

    $\Delta G < 0$. Indicates the reaction proceeds spontaneously toward equilibrium when reactants are in excess relative to products.

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