Exergonic reactions MCQs With Answer

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Exergonic reactions MCQs With Answer are essential for B. Pharm students studying biochemical thermodynamics and drug metabolism. This concise, SEO-friendly introduction covers core concepts like Gibbs free energy, spontaneity, enthalpy, entropy, activation energy, and biochemical coupling. Understanding exergonic processes helps explain ATP hydrolysis, catabolic pathways, enzyme-catalyzed reaction profiles, and redox reactions relevant to pharmacology and drug action. These MCQs are tailored to reinforce theory and problem-solving skills, linking thermodynamic principles to laboratory and clinical contexts. Clear explanations and targeted practice will boost exam readiness and conceptual clarity. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What defines an exergonic reaction?

  • The reaction absorbs free energy from the surroundings
  • The reaction releases free energy and has a negative ΔG
  • The reaction has positive enthalpy change
  • The reaction is always at equilibrium

Correct Answer: The reaction releases free energy and has a negative ΔG

Q2. Which thermodynamic quantity predicts spontaneity at constant temperature and pressure?

  • Enthalpy (ΔH)
  • Entropy (ΔS)
  • Gibbs free energy (ΔG)
  • Internal energy (ΔU)

Correct Answer: Gibbs free energy (ΔG)

Q3. For a reaction with ΔH = -50 kJ and ΔS = -100 J/K at 298 K, what is ΔG?

  • +19.8 kJ (non-spontaneous)
  • -19.8 kJ (spontaneous)
  • +80 kJ (non-spontaneous)
  • -80 kJ (spontaneous)

Correct Answer: +19.8 kJ (non-spontaneous)

Q4. How does an exergonic reaction differ from an exothermic reaction?

  • Exergonic refers to heat flow, exothermic to free energy change
  • Exergonic indicates negative ΔG, exothermic indicates negative ΔH
  • They are synonyms and always identical
  • Exergonic means non-spontaneous, exothermic means spontaneous

Correct Answer: Exergonic indicates negative ΔG, exothermic indicates negative ΔH

Q5. Which equation relates standard free energy change and equilibrium constant?

  • ΔG° = RT ln K
  • ΔG° = -RT ln K
  • ΔG = ΔH – TΔS
  • ΔG = ΔG° – RT ln Q

Correct Answer: ΔG° = -RT ln K

Q6. Which statement about catalysts is correct regarding exergonic reactions?

  • Catalysts change ΔG and make reactions more spontaneous
  • Catalysts increase activation energy
  • Catalysts lower activation energy but do not change ΔG
  • Catalysts convert exergonic to endergonic reactions

Correct Answer: Catalysts lower activation energy but do not change ΔG

Q7. In biochemical systems, which molecule commonly couples to drive endergonic reactions?

  • Glucose
  • Water
  • ATP
  • Oxygen

Correct Answer: ATP

Q8. Which expression gives ΔG under non-standard conditions?

  • ΔG = ΔH – TΔS
  • ΔG = ΔG° + RT ln Q
  • ΔG = -RT ln K
  • ΔG° = ΔG + RT ln Q

Correct Answer: ΔG = ΔG° + RT ln Q

Q9. Which of the following is an example of an exergonic biochemical process?

  • ATP synthesis driven solely by uphill reactions
  • ATP hydrolysis to ADP + Pi
  • Active transport requiring energy input
  • Protein folding that requires energy input

Correct Answer: ATP hydrolysis to ADP + Pi

Q10. What effect does increasing temperature generally have on ΔG for a reaction?

  • Always makes ΔG more negative
  • Has no effect because ΔG is independent of temperature
  • Alters ΔG via the TΔS term, effect depends on ΔS
  • Always makes ΔG more positive

Correct Answer: Alters ΔG via the TΔS term, effect depends on ΔS

Q11. If ΔG° is negative, what can be inferred about the equilibrium constant K?

  • K < 1
  • K = 1
  • K > 1
  • K = 0

Correct Answer: K > 1

Q12. Which plot best represents an exergonic reaction energy profile?

  • Products higher than reactants with a large peak
  • Products lower than reactants with a peak (activation energy)
  • Flat line with no energy difference
  • Reactants lower than products with no peak

Correct Answer: Products lower than reactants with a peak (activation energy)

Q13. Which of the following changes will make ΔG more negative for a reaction with ΔH < 0 and ΔS > 0?

  • Decrease temperature
  • Increase temperature
  • Decrease concentration of products
  • Increase pressure (for gases)

Correct Answer: Increase temperature

Q14. In the relation ΔG = -RT ln K, what does a very large positive K indicate?

  • ΔG is large and positive
  • ΔG is large and negative
  • ΔG equals zero
  • Reaction cannot occur

Correct Answer: ΔG is large and negative

Q15. Which factor does not change the sign of ΔG for a given reaction?

  • Temperature (depending on ΔS)
  • Concentrations of reactants/products
  • Presence of a catalyst
  • Pressure for gaseous reactions

Correct Answer: Presence of a catalyst

Q16. Which statement about activation energy (Ea) is true?

  • Lower Ea makes reaction faster but does not change ΔG
  • Higher Ea makes reaction faster and more spontaneous
  • Ea determines only the position of equilibrium
  • Ea is identical to ΔH for all reactions

Correct Answer: Lower Ea makes reaction faster but does not change ΔG

Q17. How is ΔG°’ (biochemical standard free energy) different from ΔG°?

  • ΔG°’ is measured at pH 7 and ΔG° at pH 0
  • ΔG°’ is measured at pH 0 and ΔG° at pH 7
  • There is no difference; they are identical
  • ΔG°’ includes enzyme effects

Correct Answer: ΔG°’ is measured at pH 7 and ΔG° at pH 0

Q18. Which term describes a reaction that proceeds with release of usable free energy?

  • Endergonic
  • Endothermic
  • Exergonic
  • Isoenergetic

Correct Answer: Exergonic

Q19. Which change would shift the reaction quotient Q to make ΔG more negative for a reaction producing product?

  • Increase product concentration
  • Decrease product concentration
  • Increase temperature regardless of ΔS
  • Add an inhibitor

Correct Answer: Decrease product concentration

Q20. ATP hydrolysis is exergonic because:

  • ATP has low-phosphate bond energy
  • Products are stabilized by resonance and hydration
  • It always absorbs heat
  • It increases order in the system

Correct Answer: Products are stabilized by resonance and hydration

Q21. Which of following is TRUE for a spontaneous exergonic reaction at constant T and P?

  • ΔG > 0
  • ΔG = 0
  • ΔG < 0
  • ΔH > 0

Correct Answer: ΔG < 0

Q22. How does coupling an endergonic reaction to ATP hydrolysis make the overall process spontaneous?

  • ATP changes ΔH of the endergonic step
  • ATP hydrolysis provides a negative ΔG so overall ΔG is negative
  • ATP increases activation energy of the endergonic step
  • Coupling destroys entropy

Correct Answer: ATP hydrolysis provides a negative ΔG so overall ΔG is negative

Q23. Which is NOT a biochemical consequence of exergonic reactions?

  • Driving active transport
  • Powering biosynthesis directly without coupling
  • Enabling muscle contraction via ATP use
  • Providing energy for signal transduction

Correct Answer: Powering biosynthesis directly without coupling

Q24. Which parameter is directly proportional to the natural logarithm of the equilibrium constant?

  • ΔS
  • ΔG°
  • ΔH
  • Activation energy

Correct Answer: ΔG°

Q25. During oxidative phosphorylation, electrons flow through ETC; how are exergonic steps used?

  • They synthesize NADH directly
  • They pump protons creating proton-motive force for ATP synthesis
  • They convert ATP into ADP
  • They produce heat without doing work

Correct Answer: They pump protons creating proton-motive force for ATP synthesis

Q26. Which phrase correctly links ΔG and spontaneity under standard conditions?

  • ΔG° = 0 indicates reaction is spontaneous
  • ΔG° < 0 indicates product-favored at equilibrium
  • ΔG° > 0 indicates reaction proceeds to completion
  • ΔG° does not relate to K

Correct Answer: ΔG° < 0 indicates product-favored at equilibrium

Q27. A reaction with ΔH < 0 and ΔS < 0 is spontaneous at:

  • High temperatures only
  • Low temperatures only
  • All temperatures
  • No temperature

Correct Answer: Low temperatures only

Q28. Which statement about biochemical standard states is correct?

  • Standard biochemical state uses [H+] = 1 M
  • Standard biochemical state uses pH 7, [H+] = 10^-7 M
  • Standard biochemical state ignores pH
  • Standard biochemical state uses 0 K temperature

Correct Answer: Standard biochemical state uses pH 7, [H+] = 10^-7 M

Q29. In living cells, why are some exergonic reactions kinetically slow?

  • Because ΔG is positive
  • Because of high activation energy barriers
  • Because enzymes remove the transition state
  • Because equilibrium constant is infinite

Correct Answer: Because of high activation energy barriers

Q30. Which best describes the transition state in an exergonic reaction?

  • Lowest free energy point along reaction coordinate
  • Highest free energy point along reaction coordinate
  • Point where products and reactants are equal
  • State with negative activation energy

Correct Answer: Highest free energy point along reaction coordinate

Q31. What is the effect of increasing reactant concentration on ΔG at constant T and P?

  • ΔG becomes more positive (less spontaneous)
  • ΔG becomes more negative (more spontaneous) if products are lower
  • ΔG is unchanged since ΔG° is fixed
  • ΔG always becomes zero

Correct Answer: ΔG becomes more negative (more spontaneous) if products are lower

Q32. Which biochemical pathway is primarily exergonic overall?

  • Gluconeogenesis
  • Glycolysis (catabolic segment)
  • Fatty acid synthesis
  • Protein synthesis

Correct Answer: Glycolysis (catabolic segment)

Q33. Which statement is true about endergonic reactions in cells?

  • They occur spontaneously without coupling
  • They require coupling to exergonic processes like ATP hydrolysis
  • They release free energy to the surroundings
  • They always have negative ΔG°

Correct Answer: They require coupling to exergonic processes like ATP hydrolysis

Q34. Which quantity increases in the surroundings when a strongly exergonic reaction occurs spontaneously?

  • System free energy
  • Surroundings entropy or heat may increase depending on ΔH
  • Overall entropy always decreases
  • Gibbs free energy of the universe decreases

Correct Answer: Surroundings entropy or heat may increase depending on ΔH

Q35. For biological redox reactions, what makes them exergonic?

  • Large positive reduction potential difference leading to negative ΔG
  • Equal potentials between donor and acceptor
  • Requirement of heat absorption
  • Decrease in entropy only

Correct Answer: Large positive reduction potential difference leading to negative ΔG

Q36. Which is a correct unit for Gibbs free energy change?

  • Mol/L
  • Joules per mole (J/mol)
  • Kelvin (K)
  • Atmosphere (atm)

Correct Answer: Joules per mole (J/mol)

Q37. A reaction with ΔG = 0 is characterized by:

  • Maximum reaction velocity
  • Equilibrium between reactants and products
  • Complete conversion to products
  • Instantaneous reaction

Correct Answer: Equilibrium between reactants and products

Q38. Which of these reduces the free energy of activation in enzyme-catalyzed exergonic reactions?

  • Raising pH to extremes
  • Formation of enzyme-substrate complex stabilizing transition state
  • Removing cofactors
  • Decreasing substrate concentration

Correct Answer: Formation of enzyme-substrate complex stabilizing transition state

Q39. How is the spontaneity of a reaction in a cell most accurately controlled?

  • By changing universal constants
  • By modifying concentrations of reactants and products and employing coupling
  • By altering ΔH only
  • By increasing atmospheric pressure universally

Correct Answer: By modifying concentrations of reactants and products and employing coupling

Q40. Which parameter directly indicates the fraction of molecules that can overcome activation energy?

  • ΔG°
  • Boltzmann factor / Arrhenius expression related to temperature and Ea
  • Equilibrium constant K only
  • ΔS only

Correct Answer: Boltzmann factor / Arrhenius expression related to temperature and Ea

Q41. In metabolic pathways, exergonic steps are often:

  • Irreversible and regulatory
  • Non-specific and futile
  • Always uncoupled from other reactions
  • Endergonic in total effect

Correct Answer: Irreversible and regulatory

Q42. Which statement about ΔG°’ for ATP hydrolysis is correct?

  • ΔG°’ is roughly +30.5 kJ/mol under biological standard conditions
  • ΔG°’ varies with cellular conditions; standard value ~ -30.5 kJ/mol
  • ΔG°’ is zero under physiological conditions
  • ΔG°’ represents activation energy

Correct Answer: ΔG°’ varies with cellular conditions; standard value ~ -30.5 kJ/mol

Q43. Which best describes coupling in biochemical terms?

  • Linking an exergonic reaction to an endergonic one to make overall ΔG negative
  • Performing two exergonic reactions separately
  • Using heat to drive both reactions
  • Preventing any net energy change

Correct Answer: Linking an exergonic reaction to an endergonic one to make overall ΔG negative

Q44. Which of the following increases spontaneity of a reaction with positive ΔH and positive ΔS?

  • Lowering temperature
  • Raising temperature
  • Removing catalysts
  • Increasing product concentration

Correct Answer: Raising temperature

Q45. Which experimental method can directly measure heat changes but not ΔG?

  • Calorimetry
  • NMR spectroscopy
  • Mass spectrometry
  • Chromatography

Correct Answer: Calorimetry

Q46. In a redox pair, a larger positive E° (standard reduction potential) for the acceptor means:

  • Electron transfer is less likely
  • Electron transfer to acceptor is more favorable and exergonic
  • No relation to ΔG
  • Reaction will be endergonic

Correct Answer: Electron transfer to acceptor is more favorable and exergonic

Q47. Which of the following is true about the sign of ΔS in exergonic reactions?

  • ΔS must always be positive
  • ΔS must always be negative
  • ΔS can be positive or negative; exergonic depends on ΔH and TΔS
  • ΔS equals ΔG for exergonic reactions

Correct Answer: ΔS can be positive or negative; exergonic depends on ΔH and TΔS

Q48. Which concept explains why coupling ATP hydrolysis to another reaction drives it forward?

  • Le Chatelier’s principle applied to single reactions
  • Addition of a catalyst removes ΔG of ATP
  • Total ΔG for coupled reactions is sum of individual ΔG values
  • ATP coupling increases activation energy of the second reaction

Correct Answer: Total ΔG for coupled reactions is sum of individual ΔG values

Q49. For a reaction at equilibrium, which is true?

  • ΔG is negative and reaction proceeds forward
  • ΔG is positive and reaction proceeds backward
  • ΔG = 0 and no net change occurs
  • Activation energy is zero

Correct Answer: ΔG = 0 and no net change occurs

Q50. Which precaution is important when applying ΔG° values to cellular metabolism?

  • ΔG° values always equal ΔG in cells
  • Cellular concentrations, pH, ionic strength and compartmentation alter actual ΔG
  • Temperature in cells is always 0 K so ΔG is undefined
  • ΔG° includes enzyme kinetics

Correct Answer: Cellular concentrations, pH, ionic strength and compartmentation alter actual ΔG

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