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 $$\Delta G \u003c 0.$$

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

$$\Delta G \u003c 0$$; 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

$$T \u003e 200\ \mathrm{K}$$

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 ($$\Delta H \u003e 0$$, $$\Delta S \u003c 0$$), 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 ($$\Delta S \u003c 0$$)?

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 $$\Delta H \u003e 0$$ and $$\Delta S \u003e 0$$?

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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