BCCB2000 Lecture 13 Questions

Question 1

Which of the following conditions would most likely predict a spontaneous reaction at low temperatures (i.e. ΔH C. ΔH > 0 D. ΔS < 0

Answer 1

A. TΔS < ΔH

Question 2

A ‘standard’ is chosen as 1M, 25°C, 1 atmosphere, and pH = 7, to describe thermodynamic parameters in biology such as Gibbs Free Energy. Why is this ‘standard’ used? A. to allow free energies to be added from different chemical reactions B. to compare the free energies from different reactions C. to allow free energies to reflect the actual conditions in the cell D. to reflect the fact that all biological reactions occur under the same conditions

Answer 2

A. to allow free energies to be added from different chemical reactions B. to compare the free energies from different reactions

Question 3

All of the following contribute to the large, negative, free-energy change upon hydrolysis of “high-energy” compounds (e.g. ATP) except: A. electrostatic repulsion in the reactant. B. stabilization of products by ionization. C. low activation energy of forward reaction D. stabilization of products by solvation. E. stabilization of products by extra resonance forms.

Answer 3

C. low activation energy of forward reaction

Question 4

If the equilibrium constant (K’eq) for a reaction is less than one (K’eq < 1.0) this means that: A. Standard Free Energy (ΔG’o) is positive and the reaction proceeds in the direction of products B. Standard Free Energy (ΔG’o) is positive and the reaction proceeds in the direction of reactants C. Standard Free Energy (ΔG’o) is negative and the reaction proceeds in the direction of reactants D. Standard Free Energy (ΔG’o) is negative and the reaction proceeds in the direction of products

Answer 4

B. Standard Free Energy (ΔG’o) is positive and the reaction proceeds in the direction of reactants

Question 5

The activation energy of a reaction: A. affects the kinetics of a reaction B. affects the entropy of a reaction C. affects the enthalpy of a reaction D. affects the Gibbs Free Energy of a reaction

Answer 5

A. affects the kinetics of a reaction

Question 6

Which of the following best describes Gibbs Free Energy (more than one option may apply) A. Accounts for only enthalpy changes in system and surroundings B. The Gibbs Free Energy predicts spontaneity of a reaction only from the properties of the system itself C. Accounts for both enthalpy and entropy changes in system and surroundings D. The Gibbs Free Energy predicts spontaneity of a reaction from the properties of the surroundings

Answer 6

B. The Gibbs Free Energy predicts spontaneity of a reaction only from the properties of the system itself C. Accounts for both enthalpy and entropy changes in system and surroundings

Question 7

Under physiological conditions the equilibrium of a metabolic reaction is affected by all of the following except: A. Concentration of substrates and products B. Concentration of the enzyme C. The energy charge (ratio of concentration of ATP and ADP) if ATP and ADP participate in the reaction D. The standard Free Energy change of the reaction E. The pH if protons are formed or consumed in the reaction

Answer 7

B. Concentration of the enzyme

Question 8

Thousands of chemical reactions occur in organisms. Consequently, it is important for us to use thermodynamics to determine if a reaction can occur spontaneously. True or False?

Answer 8

True

Question 9

Biochemical reactions are more likely to proceed if the reaction has an increase in enthalpy (△H) and a decrease in entropy (△S). True or False?

Answer 9

False

Question 10

If the equilibrium constant (K’eq) for a reaction is greater than one (K’eq > 1.0) this means that: A. Standard Free Energy (ΔG’o) is negative and the reaction proceeds in the direction of reactants B. Standard Free Energy (ΔG’o) is positive and the reaction proceeds in the direction of reactants C. Standard Free Energy (ΔG’o) is positive and the reaction proceeds in the direction of products D. Standard Free Energy (ΔG’o) is negative and the reaction proceeds in the direction of products

Answer 10

D. Standard Free Energy (ΔG’o) is negative and the reaction proceeds in the direction of products

Question 11

Which of the following statements best describe entropy (more than one option may apply) A. Tendency for reactants to be converted completely to products. B. Tendency for matter to disperse or spread out C. Tendency for heat to seek its own level D. Tendency for energy to disperse or spread out

Answer 11

B. Tendency for matter to disperse or spread out D. Tendency for energy to disperse or spread out

Question 12

In glycolysis, fructose 1,6 bisphosphate is converted to two products with a standard free-energy change ΔG’° of +23.8 kJ/mol. Under what conditions encountered in a normal cell will the free-energy change (ΔG’°) be negative, enabling the reaction to proceed spontaneously to the right? Some of the following information may be useful: ΔG’° = -RT ln Keq’; R = 8.315 J/mol·K; T in Kelvin, ΔG = ΔG’° +RTln[products]/[reactants]. ln 0.5 = -0.7, ln 2.0 = 0.7, ln 5 = 1.6, ln 20 = 3; ΔG’° = ΔH - TΔS; ΔH = -220kJ/mol) A. Under standard conditions, enough energy is released to drive the reaction to the right. B. The reaction will not go to the right spontaneously under any conditions because the ΔG’° is positive C. The reaction will proceed spontaneously to the right if there is a high concentration of products relative to the concentration of fructose 1,6 bisphosphate. D. The reaction will proceed spontaneously to the right if there is a high concentration of fructose1,6 bisphosphate relative to the concentration of products. E. None of the above conditions is sufficient.

Answer 12

D. The reaction will proceed spontaneously to the right if there is a high concentration of fructose1,6 bisphosphate relative to the concentration of products. The Free Energy of the reaction in the cell depends upon the actual concentrations of reactants and products according to the relationship: ΔG = ΔG’° + RT ln[products]/[reactants] Consequently, for the reaction to be spontaneous, where ΔG is negative, then RT ln[products]/[reactants] must be larger than ΔG’° and negative. This can be acheived in the cell by increasing the reactants (fructose1,6 bisphosphate) relative to the concentration of products.

Question 13

Which of the following statements about enthalpy are correct? A. Exothermic reactions releases enthalpy from the surroundings to the system (-ΔH) B. Endergonic reactions releases enthalpy from the system to the surroundings (-ΔH) C. Endothermic reaction absorbs energy from the surroundings into the system (+ΔH) D. Exergonic reactions absorbs enthalpy from the system to the surroundings (+ΔH) E. Exothermic reactions releases enthalpy from the system to the surroundings (-ΔH) F. Endothermic reaction absorbs energy from the system into the surroundings (+ΔH)

Answer 13

C. Endothermic reaction absorbs energy from the surroundings into the system (+ΔH) E. Exothermic reactions releases enthalpy from the system to the surroundings (-ΔH)

Question 14

Which of the following statements can be used to describe the first law of thermodynamics? (more than one option may apply) A. energy can be created and destroyed B. energy can be converted to matter in biological organisms C. energy of the universe is constant D. energy can be transferred from one form to another

Answer 14

C. energy of the universe is constant D. energy can be transferred from one form to another

Question 15

A spontaneous chemical reaction always has a ________ change. A. positive Gibbʹs free energy B. negative Gibbʹs free energy C. positive enthalpy D. negative enthalpy E. positive entropy

Answer 15

B. negative Gibbʹs free energy

Question 16

If the ΔG’o of the reaction A → B is -40 kJ/mol, under standard conditions the reaction: A. will proceed spontaneously from left to right. B. will never reach equilibrium. C. will proceed at a rapid rate. D. is at equilibrium. E. will not occur spontaneously.

Answer 16

A. will proceed spontaneously from left to right.

Question 17

Which of the following best describes Gibbs Free Energy (more than one option may apply) A. Positive Free Energy (+ΔG) means the reaction is spontaneous B. Exergonic reactions are reactions where the Free Energy is negative C. Endergonic reactions are reactions where the Free Energy is negative D. Negative Free Energy (-ΔG) means the reaction is spontaneous

Answer 17

B. Exergonic reactions are reactions where the Free Energy is negative D. Negative Free Energy (-ΔG) means the reaction is spontaneous

Question 18

Which of the following best describes Gibbs Free Energy (more than one option may apply) A. If the concentrations of products and reactants are changed then this does not affect Gibbs Free Energy. B. Free Energy describes the how far a reaction is from equilibrium C. Free energy describes the energy to do work and make changes D. Free energy does not depend upon the concentration of reactants and products.

Answer 18

B. Free Energy describes the how far a reaction is from equilibrium C. Free energy describes the energy to do work and make changes

Question 19

Which of the following best describes the activation energy of a reaction A. Depends upon the path taken from initial to final states of the reaction B. Decreased by enzymes and other catalysts C. The same as the enthalpy or entropy for a reaction D. Delays the progress of a spontaneous chemical reaction

Answer 19

A. Depends upon the path taken from initial to final states of the reaction B. Decreased by enzymes and other catalysts D. Delays the progress of a spontaneous chemical reaction

Question 20

Free energy is the result of two different thermodynamic ‘driving forces’. The relationship between Free energy and these two forces is expressed in the following equation: A. ΔS = ΔH + TΔG B. ΔH = ΔG + TΔS C. ΔG = ΔH - TΔS D. ΔG = ΔH + TΔS E. ΔG = ΔH + ΔS

Answer 20

C. ΔG = ΔH - TΔS

Question 21

Which of the following applies to most organisms (more than one option may apply): A. Are highly disorded so as to not contravene the Second Law of Thermodynamics B. Organisms are always at equilibrium with surroundings C. Organisms constantly transfer matter and energy with their surroundings D. Always obey the Laws of Thermodynamics

Answer 21

C. Organisms constantly transfer matter and energy with their surroundings D. Always obey the Laws of Thermodynamics

Question 22

For the reaction A → B, ΔG’° = -6 kJ/mol. The reaction is started with 10 mmol of A; no B is initially present. After 24 hours, analysis reveals the presence of 2 mmol of B, 8 mmol of A. Assume that there is no significant volume change during the reaction. Which of the following is the most likely explanation? A. A and B have reached equilibrium concentrations. B. Formation of B is thermodynamically unfavorable. C. The result described is impossible, given the fact that ΔG’° is -60 kJ/mol. D. equilibrium has not been reached by 24 hours. E. An enzyme has shifted the equilibrium toward A.

Answer 22

D. equilibrium has not been reached by 24 hours.

Question 23

Organisms may use energy to do the following (more than one option may apply): A. move ions across membranes against their concentration gradient B. breakdown carbon containing compounds to inorganic compounds C. convert carbon containing compounds to other carbon containing compounds. D. move from one location to another

Answer 23

A. move ions across membranes against their concentration gradient B. breakdown carbon containing compounds to inorganic compounds C. convert carbon containing compounds to other carbon containing compounds. D. move from one location to another

Question 24

How much heat energy could be released by the compete hydrolysis of ATP under standard conditions (ΔG’o = -30.5 kJ/nol) where the reaction is not coupled to any other reaction and the energy remaining in the products is 14.6kJ/mol? A. -15.9 kJ/mol B. -45.1 kJ/mol C. + 15.9 kJ/mol D. +45.1 kJ/mol

Answer 24

A. -15.9 kJ/mol ΔG = ΔH - TΔS ΔG’o = -30.5kJ/mol -30.5 = ΔH - TΔS Energy remaining in products = TΔS = +14.6 -30.5 = ΔH - (+14.6) -30.5 = ΔH - 14.6 -30.5 + 14.6 = -15.9 = ΔH At constant pressure and volume ΔH = q (heat) Amount of heat released = ΔH = -15.9 kJ/mol

Question 25

The standard free-energy changes for the reactions below are given: Phosphocreatine ---> creatine + Pi ΔG'° = -43.0 kJ/mol ATP ---> ADP + Pi ΔG'° = -30.5 kJ/mol What is the overall ΔG'° for the following reaction? Phosphocreatine + ADP ---> creatine + ATP A. ΔG'° = -12.5 kJ/mol B. ΔG'° = +12.5 kJ/mol C. ΔG'° = -73.5 kJ/mol D. ΔG'° = +73.5 kJ/mol E. ΔG'° cannot be calculated without Keq'

Answer 25

## Footnote A. ΔG'° = -12.5 kJ/mol Free energy values can be summed. In this case the ATP reaction occurs in reverse and so the Free energy value must have its sign changed from negative to positive. ΔG'° = -43 + 30.5 = -12.5 kJ/mol

Question 26

Determine if the statement and reason are true. Is the reason a correct explanation of the statement? Statement: In most biological systems we find that the variables used to describe a thermodynamic system are: pressure, volume and temperature are always changing. Reason: Most reactions in organisms occur in solutions.

Answer 26

## Footnote Statement is False; Reason is True

Question 27

Which of the following statements best describe entropy (more than one option may apply) A. Entropy of solution (a mixture) is less than the entropy of pure solvent or solute B. Entropy of solution (a mixture) is greater than the entropy of pure solvent or solute C. Entropy gas entropy of liquid > entropy of solid (where > means 'greater than')

Answer 27

## Footnote B. Entropy of solution (a mixture) is greater than the entropy of pure solvent or solute D. Entropy gas > entropy of liquid > entropy of solid (where > means 'greater than')

Question 28

If 100kJ of heat energy were transferred into a bacterium and the bacterium was considered the thermodynamic 'system' then this would mean: A. -100kJ of energy was 'lost' from the surroundings B. +100kJ of energy was transferred to the surroundings C. +100kJ of energy was 'lost' from the surroundings D. -100kJ of energy was transferred to the system

Answer 28

## Footnote C. +100kJ of energy was 'lost' from the surrounding

Question 29

The oxidation of glucose is exothemic and can be represented by the following equation C6H12O6 + 6O2 → 6CO2 + 6H2O From the list below choose the most likely options that apply to this reaction. There may be one, or more than one, correct choice. A. Entropy seems to increase because there are more molecules of products compared with reactants B. Entropy seems to increase because the reaction has an overall -ΔS value C. Entropy seems to decrease because there are more molecules of products compared with molecules of reactants D. The reaction is likely to be spontaneous because there is -ΔH E. The reaction is likely to be spontaneous because there is +ΔH F. The reaction is likely to be spontaneous because there is -ΔH and +ΔS G. The reaction is likely to be spontaneous because there is +ΔH and +ΔS

Answer 29

## Footnote A. Entropy seems to increase because there are more molecules of products compared with reactants F. The reaction is likely to be spontaneous because there is -ΔH and +ΔS

Question 30

Consider the following reaction: A + B → C + D ΔG'o = +20 kJmol-1 If the cellular concentrations are:[A] = 5mM, [B] = 10mM, [C] = 5mM, [D] = 3mM Calculate the Free Energy change for the reaction at 25°C (to three significant figures). Some or all of the following information may be useful for this question: Faraday Constant (F): F=96.48 kJV-1mol-1, Gas constant (R): R=8.315 J/mol/K; Temperature is Kelvin A. -23.7 kJmol-1 B. -27.5 kJmol-1 C. +12.2 kJmol-1 D. -35.3 kJmol-1 E. +17.0 kJmol-1

Answer 30

## Footnote E. +17.0 kJmol-1 You need to use the relationship: ΔG = ΔG'o + RTln ([C][D]/[A][B]) This relationship can be considered a 'dilution' of the standard Free Energy, because we are using actual concentrations and not standard concentrations (1M). Temperature has to be converted to Kelvin: 273 + 25 = 298K ΔG = 20000 + (8.315 x 298) x ln ([5][3]/[10][5]) ΔG = 20000 + (8.315 x 298) x ln ([5][3]/[10][5]) ΔG = 20000 + (2478 x ln (15/50)) ΔG = 20000 + (2478 x -1.2) = 20000 - 2974 = +17026 = +17.0kJ/mol (3 sig fig)

Question 31

When a mixture of glucose-6-phosphate and fructose-6-phosphate is incubated with the enzyme phosphohexose isomerase (which catalyzes the interconversion of these two compounds. until equilibrium is reached at 25°C, the final mixture contains twice as much glucose-6-phosphate as fructose-6-phosphate. Which one of the following statements is most nearly correct, when applied to the reaction below? Glucose-6-phosphate → fructose-6-phosphate ΔG'° = -RT ln Keq'; Gas constant (R): R=8.315 x JK-1mol-1; ln0.5 = -0.7; ln0.7=-0.4; ln2=0.7 A. ΔG'° is +1.73 kJ/mol. B. ΔG'° is zero. C. ΔG'° is -1.73 kJ/mol. D. ΔG'° is very large and negative. E. ΔG'° is very large and positive.

Answer 31

## Footnote A. ΔG'° is +1.73 kJ/mol Keq = [fructose-6-phosphate]/[glucose-6-phosphate] Keq = [1]/[2] (In this case the units of concentration such as M would cancel out and you are left with a ratio of numbers) Keq = 0.5 ln Keq = -0.7 (given to you). 25°C = 298 Kelvin Thus: ΔG'° = -RT ln Keq' ΔG'° = -8.315 x 298 x -0.7 ΔG'° = +1734 J/mol = +1.734 kJ/mol

Question 32

Conversion of glucose-6-phosphate to fructose-6-phosphate is catalyzed by phosphohexose isomerase and is 33% complete at equilibrium under standard biochemical conditions. Calculate the free energy of this reaction using R = 8.315 J/K/mol. A. ΔG'o = -2.75 kJ/mol B. ΔG'o = -1.70 kJ/mol C. ΔG'o = +1.76 kJ/mol D. ΔG'o = -1755 kJ/mol E. ΔG'o = -1.76 kJ/mol F. ΔG'o = +2.75 kJ/mol G. ΔG'o = +1755 kJ/mol

Answer 32

## Footnote C. ΔG'o = +1.76 kJ/mol If the reaction is 33% complete this means that product = 33% and reactant =67% Standard conditions are T = 25°C or 298K, and pH=7 and hence need to use the following formula for standard ΔG Use the formula ΔG'o = -RTlnKeq ΔG'o = -8.315 x 298 x ln33/67 ΔG'o = -2477.87 x ln0.4925 ΔG'o = -2477.87 x -0.70818 ΔG'o = +1755 J/mol = 1.76 kJ/mol (3 sig fig)

Question 33

When Keq of a reaction = 1, then A. the forward reaction is faster than the reverse reaction. B. the reverse reaction is faster than the forward reaction. C. the forward and reverse reaction rate constants are equal. D. more products are formed than reactants. E. fewer products are formed than reactants.

Answer 33

## Footnote C. the forward and reverse reaction rate constants are equal.

Question 34

The entropy of living organsims is low and this suggests that: A. Living organisms have low entropy due, in part, to the intake of heat energy from the surroundings B. Living organisms do not obey the second law of thermodynamics C. The laws of thermodynamics allow high complexity and organisation in living organisms D. Living organisms have low entropy due, in part, to the release of heat energy to the surroundings

Answer 34

## Footnote C. The laws of thermodynamics allow high complexity and organisation in living organisms D. Living organisms have low entropy due, in part, to the release of heat energy to the surroundings

Question 35

Thousands of chemical reactions occur in organisms. Consequently, it is important for us to use kinetics to determine if a reaction can occur spontaneously. True or False?

Answer 35

## Footnote False

Question 36

Which of the following conditions (select each appropriate condition) would most likely predict a spontaneous reaction at low temperatures and ΔS 0 C. ΔH ΔH

Answer 36

## Footnote C. ΔH < 0

Question 37

Which of the following conditions would most likely predict a spontaneous reaction at 298K (25°C): A. ΔH > 0 and ΔS 0 C. ΔH 0

Answer 37

## Footnote B. ΔH 0