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Reactions differ from many physical processes in that they may proceed:
AIn both forward and reverse
BOnly in the forward direction
COnly in the reverse direction
DIn neither direction ever
Answer & Solution
Correct answer: A. In both forward and reverse
1. A single arrow suggests a one-way change, which is often an approximation.
2. Reactions may proceed in both forward, left to right, and reverse, right to left, directions.
3. Physical changes such as phase transitions are also reversible and may establish equilibria.
4. The vapour pressure of a condensed phase is one familiar example of such an equilibrium.
5. Reversibility is what makes an equilibrium constant meaningful at all.
_Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 13 'Fundamental Equilibrium Concepts', sections 13.1-13.4_
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