Q: A reaction has $$\Delta H = -100 kJ/$$mol and $$\Delta S = +0.2 kJ/($$mol\cdot K). At $$T = 300 K$$, what is $$\Delta G$$ for the reaction?

$$\Delta G = -100 - (300 \times 0.2) = -160 kJ/$$mol

Q: A cell uses the breakdown of glucose ($$\Delta G = -2870 kJ/$$mol) to power the synthesis of ATP ($$\Delta G = +30.5 kJ/$$mol). What is the net $$\Delta G$$ for the coupled reaction if 1 mol of glucose is used to make 30 mol of ATP?

$$\Delta G = -2870 + (30 \times 30.5) = -2870 + 915 = -1955 kJ/$$mol

Question 1

Which of the following best describes a spontaneous chemical reaction in terms of free energy?

Accepted Answer

It occurs without input of energy and $$\Delta G \u003c 0.$$

Question 2

Which equation correctly relates free energy change ($$\Delta G$$), enthalpy change ($$\Delta H$$), temperature ($$T$$), and entropy change ($$\Delta S$$)?

Accepted Answer

$$\Delta G = \Delta H - T \Delta S$$

Question 3

A reaction has $$\Delta H = -100 kJ/$$mol and $$\Delta S = +0.2 kJ/($$mol\cdot K). At $$T = 300 K$$, what is $$\Delta G$$ for the reaction?

Accepted Answer

$$\Delta G = -100 - (300 	imes 0.2) = -160 kJ/$$mol

Question 4

Why is metabolism in living cells never at equilibrium?

Accepted Answer

Because equilibrium would mean no net change and no work could be done.

Question 5

Which of the following statements about exergonic and endergonic reactions is correct?

Accepted Answer

Exergonic reactions have $$\Delta G \u003c 0$$ and release energy.

Question 6

A cell uses the breakdown of glucose ($$\Delta G = -2870 kJ/$$mol) to power the synthesis of ATP ($$\Delta G = +30.5 kJ/$$mol). What is the net $$\Delta G$$ for the coupled reaction if 1 mol of glucose is used to make 30 mol of ATP?

Accepted Answer

$$\Delta G = -2870 + (30 	imes 30.5) = -2870 + 915 = -1955 kJ/$$mol

Question 7

Which of the following best explains why water flowing downhill can power a generator, but only until the system reaches equilibrium?

Accepted Answer

Because once equilibrium is reached, there is no longer a free energy difference to drive work.

Question 8

If a reaction in a cell has $$\Delta G = +15 kJ/$$mol, what must happen for the reaction to proceed?

Accepted Answer

It must be coupled to an exergonic reaction with $$\Delta G \u003c 0.$$

Question 9

Which of the following is a real-life example of an open system maintaining non-equilibrium to perform work?

Accepted Answer

A cell using nutrients and expelling waste to keep metabolic reactions going.

Question 10

Which of the following would increase the likelihood that a reaction is spontaneous?

Accepted Answer

A decrease in enthalpy ($$\Delta H  0).$$

Question 11

Why is the free energy change ($$\Delta G) $$important in predicting the direction of metabolic reactions?

Accepted Answer

Because only reactions with $$\Delta G \u003c 0$$ can occur spontaneously and drive cellular processes.

Question 12

Which statement about equilibrium and metabolism is correct?

Accepted Answer

Metabolism is never at equilibrium because cells are open systems exchanging matter and energy.

Question 13

A reaction has $$\Delta H = +50 kJ/$$mol and $$\Delta S = +0.3 kJ/($$mol\cdot K). At what temperature will the reaction become spontaneous?

Accepted Answer

When $$T \u003e \frac{\Delta H}{\Delta S} = \frac{50}{0.3} \approx 167 K$$

Question 14

Which of the following is true about the relationship between free energy and stability?

Accepted Answer

Lower free energy means greater stability in a system.

Question 15

Which process in living cells is an example of an exergonic reaction?

Accepted Answer

The hydrolysis of ATP to ADP and phosphate.

Question 16

If a cell reaches metabolic equilibrium, what is the consequence?

Accepted Answer

The cell can no longer perform work and will die.

Free Energy Change and Spontaneity in Biological Reactions

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