Which of the following is spontaneous reaction?
Correct answer: A. Zn + Cu²+ → Zn²+ + Cu
- A. Zn + Cu²+ → Zn²+ + Cu
- B. Fe + H2O → Fe2+ + OH-
- C. 2H2 + O2 → 2H2O
- D. Ag+ + Cl- → AgCl
Explanation
The correct answer is the reaction Zn + Cu²+ → Zn²+ + Cu. This reaction is spontaneous because it has a positive standard cell potential (E°). The reduction potential of Cu²+ (+0.34V) is greater than that of Zn²+ (-0.76V), indicating that Cu²+ is a stronger oxidizing agent than Zn²+. Therefore, Cu²+ can oxidize Zn, making the reaction spontaneous.The other options are incorrect because they do not meet the criteria for spontaneity under standard conditions. Option B involves Fe and water, which do not react spontaneously. Option C (2H2 + O2 → 2H2O) is not spontaneous without external energy input, and Option D (Ag+ + Cl- → AgCl) does not lead to a positive cell potential under standard conditions.
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About Redox Reactions
Redox reactions involve oxidation and reduction occurring together, with electrons transferred between species or oxidation numbers changing. The topic covers assigning oxidation states, identifying oxidizing and reducing agents, balancing redox equations by oxidation number or half-reaction methods, and connecting chemical changes with galvanic and electrolytic cells.
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