Question 1

Which of the following best describes an open thermodynamic system?

Accepted Answer

A system that can exchange both energy and matter with its surroundings.

Question 2

Which equation correctly represents the relationship between Gibbs free energy, enthalpy, and entropy at constant temperature and pressure?

Accepted Answer

$$G = H - TS$$

Question 3

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

Accepted Answer

$$T = 500\ \mathrm{K}$$

Question 4

Which of the following statements about reversible and irreversible processes is correct?

Accepted Answer

A reversible process occurs near equilibrium, while an irreversible process is far from equilibrium.

Question 5

According to the second law of thermodynamics, what happens to the entropy of an isolated system?

Accepted Answer

It tends to increase to a maximum value.

Question 6

For the reaction $$A + B \rightleftharpoons C + D$$, the equilibrium constant $$K is $$given by:

Accepted Answer

$$K = \frac{[C][D]}{[A][B]}$$

Question 7

Which of the following best explains why the hydrolysis of phosphoenolpyruvate (PEP) is more exergonic than the hydrolysis of ATP?

Accepted Answer

PEP hydrolysis products are stabilized by resonance and tautomerization.

Question 8

If a reaction has $$\Delta G \u003c 0$$, which of the following is true?

Accepted Answer

The reaction is thermodynamically favorable and can proceed spontaneously.

Question 9

In a living cell, homeostasis is maintained by keeping the reaction quotient $$Q$$:

Accepted Answer

Far from the equilibrium constant $$K$$

Question 10

Which of the following is a correct statement about the coupling of unfavorable and favorable reactions in biological systems?

Accepted Answer

An unfavorable reaction can proceed if it is coupled to a favorable reaction with a sufficiently negative $$\Delta G.$$

Question 11

Which of the following equations correctly relates the free energy change to the reaction quotient $$Q$$ and the equilibrium constant $$K$$?

Accepted Answer

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

Question 12

A cell maintains a concentration of ion A such that $$[A]_1 = 0.01\ \mathrm{M}$$ inside and $$[A]_2 = 0.1\ \mathrm{M}$$ outside. What is the sign of $$\Delta G$$ for the passive transport of A from inside to outside?

Accepted Answer

$$\Delta G is $$negative; the process is favorable.

Question 13

Which of the following best describes the role of ATP in cellular metabolism?

Accepted Answer

ATP acts as a common energy currency, coupling exergonic and endergonic reactions.

Question 14

Which of the following statements about standard reduction potential ($$E^\circ) is $$correct?

Accepted Answer

A higher $$E^\circ$$ means a greater tendency to gain electrons and be reduced.

Question 15

Which of the following is true for a reaction at equilibrium?

Accepted Answer

$$\Delta G = 0$$

Question 16

A reaction has $$\Delta G^\circ = +1.7\ \mathrm{kJ/mol}. If $$the concentrations of products are much lower than reactants, what can be said about $$\Delta G$$?

Accepted Answer

$$\Delta G$$ can be negative if $$Q is $$sufficiently small.

Question 17

Which of the following is NOT a reason why the hydrolysis of ATP is exergonic?

Accepted Answer

ATP hydrolysis increases charge repulsion in the products.

Question 18

Which of the following best describes homeostasis in living systems?

Accepted Answer

Homeostasis maintains steady-state concentrations of metabolites far from equilibrium.

Question 19

If $$Q \u003c K$$ for a chemical reaction, what is the direction of the reaction and the sign of $$\Delta G$$?

Accepted Answer

The reaction proceeds forward (toward products) and $$\Delta G \u003c 0.$$

Question 20

Which of the following is a real-life example of coupling an unfavorable reaction to a favorable one in biological systems?

Accepted Answer

Synthesis of glucose-6-phosphate from glucose and ATP during glycolysis.

Free Energy and Thermodynamics in Biological Systems

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