Q: A reaction has $$\Delta H = -50 kJ/$$mol and $$\Delta S = -0.1 kJ/($$mol\cdot K)$$. At T = 298$ K, what is $$\Delta G$$? Use $$\Delta G = \Delta H - T\Delta S$.

$$\Delta G = -50 - (298 \times -0.1) = -50 + 29.8 = -20.2 kJ/$$mol

Question 1

Which of the following best describes the main difference between phototrophs and chemotrophs?

Accepted Answer

Phototrophs use sunlight as their primary energy source, while chemotrophs obtain energy by oxidizing chemical bonds in molecules.

Question 2

Which of the following is an example of mechanical work in cells?

Accepted Answer

The movement of chromosomes along spindle fibers during mitosis.

Question 3

A cell accumulates glucose against its concentration gradient. This is an example of:

Accepted Answer

Concentration work

Question 4

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

Accepted Answer

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

Question 5

Which of the following statements about the first law of thermodynamics is correct?

Accepted Answer

The total amount of energy in the universe remains constant during any physical or chemical change.

Question 6

A reaction has $$\Delta H = -50 kJ/$$mol and $$\Delta S = -0.1 kJ/($$mol\cdot K)$$. At T = 298$ K, what is $$\Delta G$$? Use $$\Delta G = \Delta H - T\Delta S$.

Accepted Answer

$$\Delta G = -50 - (298 	imes -0.1) = -50 + 29.8 = -20.2 kJ/$$mol

Question 7

Which of the following best explains why cells are considered open systems?

Accepted Answer

They can exchange both energy and matter with their surroundings.

Question 8

Which of the following is true about exergonic reactions?

Accepted Answer

They have a negative $$\Delta G$$ and occur spontaneously.

Question 9

In the oxidation of glucose ($$C_6H_{12}O_6$ + 6O_2 \rightarrow 6CO_2 + 6H_2O$$), the standard free energy change ($$\Delta G) is$$ $$-686$$ kcal/mol. What does this indicate about the reaction?

Accepted Answer

The reaction is exergonic and releases energy.

Question 10

A reaction has an equilibrium constant $$K'_{eq} = 0.1 at $$standard conditions. What can you conclude about $$\Delta G$$^{\circ\prime}$$?

Accepted Answer

$$\Delta G$$^{\circ\prime}$$ is positive and the reaction favors reactants.

Question 11

Which of the following best describes the role of entropy ($$\Delta S) in $$biological reactions?

Accepted Answer

A positive $$\Delta S$$ increases disorder and can contribute to making a reaction spontaneous.

Question 12

Which of the following is NOT a form of biological work that requires energy?

Accepted Answer

Passive diffusion of oxygen into a cell

Question 13

A cell maintains a steady state by:

Accepted Answer

Continuously exchanging energy and matter with its environment to keep reactions far from equilibrium.

Question 14

Which of the following equations correctly relates the equilibrium constant ($$K_{eq}) to $$the standard free energy change ($$\Delta G$$^{\circ}$$) at 25°C?

Accepted Answer

$$\Delta G$$^{\circ}$$ = -RT \ln K_{eq}$$

Question 15

Which of the following is a real-life example of electrical work in biological systems?

Accepted Answer

The pumping of Na+ and K+ ions across a neuron membrane to generate an action potential

Question 16

If a reaction in a cell has $$\Delta G' = 0$$, what does this indicate?

Accepted Answer

The reaction is at equilibrium under the given cellular conditions.

Question 17

Which of the following best explains why heat is not a useful energy source for most cellular processes?

Accepted Answer

Cells are isothermal, so heat flow does not drive most cellular reactions.

Question 18

Which of the following is a correct statement about the relationship between $$\Delta G$$ and the direction of a reaction?

Accepted Answer

If $$\Delta G \u003c 0$$, the reaction proceeds spontaneously in the forward direction.

Question 19

A scientist measures the concentrations of glucose-6-phosphate and fructose-6-phosphate in a cell as 83 μM and 14 μM, respectively. If $$\Delta G$$^{\circ\prime}$$ = +410$$ cal/mol and $$RT = 592$$ cal/mol, what is the actual $$\Delta G'$$ for the reaction: glucose-6-phosphate $$ightarrow$$ fructose-6-phosphate? (Use $$\Delta G' = \Delta G$$^{\circ\prime}$$ + RT \ln \frac{[	ext{fructose-6-phosphate}]}{[	ext{glucose-6-phosphate}]})$$

Accepted Answer

$$\Delta G' = 410 + 592 \ln(14/83) = 410 + 592 \ln(0.169) = 410 + 592 	imes (-1.78) = 410 - 1054 = -644$$ cal/mol

Bioenergetics: The Flow of Energy in the Cell – Study Notes

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