ATP energetics: Approximately how much free energy (under standard biochemical conditions) is released by hydrolysis of one mole of ATP to ADP + Pi?

Introduction / Context: ATP hydrolysis drives countless cellular reactions by coupling. The magnitude of free energy change is important for assessing whether a coupled process can proceed spontaneously.

Given Data / Assumptions:

• Standard biochemical conditions (pH 7, 25°C, 1 M activities) give a reference ΔG°'.
• In vivo ΔG can be more negative due to actual ATP/ADP/Pi ratios and Mg2+ binding.
• We use the commonly cited textbook value for ΔG°'.

Concept / Approach: The widely accepted standard free energy change for ATP → ADP + Pi is approximately −7.3 kcal/mol (−30.5 kJ/mol). This value allows rough comparisons of energy costs and yields across metabolic steps.

Step-by-Step Solution: Recall the typical ΔG°' magnitude. Eliminate unrealistic options in the tens to thousands of kcal/mol. Select the value closest to −7.3 kcal/mol by magnitude (reporting absolute magnitude here). Choose 7.3 kcal.

Verification / Alternative check: Biochemistry references list −7 to −8 kcal/mol under standard conditions; cellular ΔG can reach −10 to −12 kcal/mol depending on concentrations.

Why Other Options Are Wrong: 76, 760, and 1000 kcal are orders of magnitude too large; 0.73 kcal is too small to power most biochemical work.

Common Pitfalls: Confusing ΔG°' with in vivo ΔG; forgetting units (kcal vs kJ).

Final Answer: 7.3 kcal.