Q: A cell needs to drive the reaction $X \rightarrow Y$ with $\Delta G^\circ = +15\ \mathrm{kJ/mol}$. Which strategy would NOT help make this reaction proceed in the forward direction?

Increasing the concentration of Y.

Q: Which of the following is true regarding the biochemical standard state ($\Delta G^\circ'$) compared to the chemical standard state ($\Delta G^\circ$)?

In the biochemical standard state, $[H^+] = 10^{-7}\ \mathrm{M}$ (pH 7) and the activity of water is set to 1.

Q: For the reaction $A + B \rightleftharpoons C + D$, the actual free energy change is given by:

$\Delta G = \Delta G^\circ + RT \ln Q$

Q: Which of the following best describes an exergonic reaction?

$\Delta G < 0$; the reaction is spontaneous and releases free energy.

Q: If a reaction is both enthalpically and entropically opposed ($\Delta H > 0$, $\Delta S < 0$), what can be said about its spontaneity?

It is non-spontaneous at all temperatures.

Question 1

Which of the following statements best describes the relationship between entropy ($\Delta S$) and the physical state of a substance?

Accepted Answer

Entropy decreases as a substance changes from gas to liquid to solid.

Question 2

A reaction has $\Delta H = -50\ \mathrm{kJ/mol}$ and $\Delta S = -100\ \mathrm{J/(mol\cdot K)}$. At what temperature (in Kelvin) does this reaction change from spontaneous to non-spontaneous?

Accepted Answer

$T = 500\ \mathrm{K}$

Question 3

Which of the following best explains why biological systems must avoid reaching equilibrium?

Accepted Answer

At equilibrium, no free energy is available to do work, leading to cell death.

Question 4

Given the reaction $A + B \rightleftharpoons C + D$, if $K = 10$ and $Q = 0.1$, what can be inferred about the direction of the reaction and the sign of $\Delta G$?

Accepted Answer

The reaction will proceed forward and $\Delta G < 0$.

Question 5

Which of the following equations correctly relates the standard free energy change ($\Delta G^\circ$) to the equilibrium constant ($K$)?

Accepted Answer

$\Delta G^\circ = -RT \ln K$

Question 6

A cell needs to drive the reaction $X \rightarrow Y$ with $\Delta G^\circ = +15\ \mathrm{kJ/mol}$. Which strategy would NOT help make this reaction proceed in the forward direction?

Accepted Answer

Increasing the concentration of Y.

Question 7

Which of the following is true regarding the biochemical standard state ($\Delta G^\circ'$) compared to the chemical standard state ($\Delta G^\circ$)?

Accepted Answer

In the biochemical standard state, $[H^+] = 10^{-7}\ \mathrm{M}$ (pH 7) and the activity of water is set to 1.

Question 8

For the reaction $A + B \rightleftharpoons C + D$, the actual free energy change is given by:

Accepted Answer

$\Delta G = \Delta G^\circ + RT \ln Q$

Question 9

Which of the following best describes an exergonic reaction?

Accepted Answer

$\Delta G < 0$; the reaction is spontaneous and releases free energy.

Question 10

A reaction has $\Delta H = +20\ \mathrm{kJ/mol}$ and $\Delta S = +100\ \mathrm{J/(mol\cdot K)}$. At what temperature does the reaction become spontaneous?

Accepted Answer

$T > 200\ \mathrm{K}$

Question 11

Which of the following is a correct statement about the effect of entropy on reaction spontaneity?

Accepted Answer

A positive $\Delta S$ increases the likelihood that a reaction is spontaneous, especially at higher temperatures.

Question 12

Which of the following best describes the effect of coupling a non-spontaneous reaction to ATP hydrolysis in a cell?

Accepted Answer

The overall $\Delta G$ for the coupled reactions becomes negative, allowing the non-spontaneous reaction to proceed.

Question 13

If a reaction is both enthalpically and entropically opposed ($\Delta H > 0$, $\Delta S < 0$), what can be said about its spontaneity?

Accepted Answer

It is non-spontaneous at all temperatures.

Question 14

Which of the following scenarios would result in a decrease in entropy ($\Delta S < 0$)?

Accepted Answer

Condensation of water vapor to liquid water.

Question 15

A reaction has $\Delta G = 0$. Which of the following is true?

Accepted Answer

The reaction is at equilibrium and no net change occurs.

Question 16

Which of the following is NOT a way to drive an unfavorable reaction in a cell?

Accepted Answer

Increasing the concentration of products.

Question 17

Which of the following best describes the effect of temperature on the spontaneity of a reaction with $\Delta H > 0$ and $\Delta S > 0$?

Accepted Answer

The reaction becomes spontaneous at high temperatures.

Question 18

Which of the following is the correct expression for the reaction quotient $Q$ for the reaction $aA + bB \rightleftharpoons cC + dD$?

Accepted Answer

$Q = \dfrac{[C]^c [D]^d}{[A]^a [B]^b}$

Biochemical Thermodynamics: Principles and Applications

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