The ∆Gº is a _______________ value often written in textbooks. The _______________ is used in cellular conditions because varying temperature and a high amount of _______________ may make even a ______________ ∆Gº reaction spontaneous. (overthrowing the natural favorability/non-favorability).

Question

BlackTom AI · Accepted Answer

ΔG° is an experimental, essentially unchanging, standard free-energy value determined under defined standard conditions (1 M, 1 atm, 25 °C) and is what you find tabulated in textbooks. The cellular free-energy change, written as ΔG (here represented by ΔG(n) in the answer), is used in vivo because actual cellular temperature and, more importantly, reactant and product concentrations differ from standard conditions. A high concentration of reactant can drive a reaction that has a positive ΔG° to proceed spontaneously in the cell.

Relevant concepts
- ΔG° (standard free energy) is a constant for a given reaction at specified standard conditions and is measured experimentally.
- ΔG (actual/physiological free energy) depends on concentrations and temperature: ΔG = ΔG° + RT ln Q, where Q = [products]/[reactants].
- If Q is small (lots of reactant relative to product), ln Q is negative and RT ln Q can be sufficiently negative to overcome a positive ΔG°.

Step-by-step reasoning with a numeric example
1. Start with ΔG = ΔG° + RT ln Q.
2. Choose ΔG° = +5.0 kJ·mol⁻¹ (a positive standard free energy).
3. Use R = 8.314 J·mol⁻¹·K⁻¹ = 0.008314 kJ·mol⁻¹·K⁻¹ and T = 298 K.
4. Suppose cellular Q = 10⁻6 (very high reactant concentration relative to product), so ln Q = ln(10⁻6) = −13.8155.
5. Compute RT ln Q = 0.008314 × 298 × (−13.8155) = −34.3 kJ·mol⁻¹.
6. Then ΔG = +5.0 + (−34.3) = −29.3 kJ·mol⁻¹ (negative → spontaneous under cellular conditions).

Why the correct answer is correct
- ΔG° is experimentally determined and treated as unchanging for standard conditions; ΔG (ΔG(n) in the answer) is the physiological value used in cells. High reactant concentration (not product) can make a reaction with a positive ΔG° spontaneous by making Q very small and RT ln Q strongly negative.

Why the other options are incorrect
- Option 1: says ΔG° is “changing/cellular” — incorrect because ΔG° refers to standard (unchanging) conditions.
- Option 2: swaps reactant/product and sign — the key driver is high reactant concentration, not product, and the scenario describes overcoming a positive ΔG°.
- Option 4: again mislabels ΔG° as changing/cellular and misidentifies the cellular term.

Conclusion
All reasoning supports the provided answer: experimental/unchanging, ΔG(n), Reactant, positive.

The ∆Gº is a _______ value often written in textbooks. The _ is used in cellular conditions because varying temperature and a high amount of _ may make even a ______ ∆Gº reaction spontaneous. (overthrowing the natural favorability/non-favorability).单项选择题

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