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Predicting Redox Reactions

some oxidation reactions occur spontaneously while others require the input of energy

Zn _(s) + Cu²⁺ _(aq) → Zn²⁺ _(aq)+ Cu (s)
Zn²⁺ _(aq) + Cu (s) → no reaction

the spontaneity of a reaction depends on the strength of the oxidizing agent (the species that is reduced) and the reducing agent (the thing that is oxidized)
once the spontaneity of a number of half reactions are known, can list them in terms of their oxidizing and reducing strength – Appendix C11 pg 805

redox spontaneity rule a spontaneous redox reaction occurs only if the oxidizing agent (OA) is above the reducing agent (RA) in a table of relative strengths of oxidizing agents and reducing agents

example: In a school laboratory four metals were combined with each of four solutions. Construct a table of relative strength of oxidizing and reducing agents.
Be _(s) + Cd²⁺ _(aq) Cd _(s) + 2 H+ _(aq) Ca²⁺_(aq) + Be _(s) Cu _(s) + H+ _(aq)	→ → → →	Be2+ _(aq) + Cd _(s) Cd²⁺ _(aq) + H₂_(g) no evidence of reaction no evidence of reaction
Since Cd²⁺ can take electrons from Be (s), causing Be (s) to be oxidized, Cd²⁺ is a stronger oxidizing agent
		Cd²⁺ _(aq) + 2e- Be²⁺ _(aq) + 2e-	→ →	Cd _(s) Be _(s)
Since H+ can take electrons from Cd (s), causing Cd (s) to be oxidized, H+ is a stronger oxidizing agent
		2 H²⁺ _(aq) + 2e- Cd⁺ _(aq) + 2e-	→ →	H₂_(g) Cd _(s)
Since Ca²⁺ cannot take electrons from Be (s), than Ca²⁺ is a weaker oxidizing agent than Be
		Be²⁺ _(aq) + 2e- Ca²⁺ _(aq) + 2e-	→ →	Be _(s) Ca _(s)
Since H+ cannot take electrons from Cu, than H⁺ is a weaker oxidizing agent than Cu
		Cu²⁺ _(aq) + 2e- 2 H⁺ _(aq) + 2e	→ →	Cu _(s) H₂_(g)
Can combine all of this into:
	SOA	Cu²⁺ _(aq) + 2e- 2 H⁺ _(aq) + 2e- Cd²⁺ _(aq) + 2e- Be²⁺ _(aq) + 2e- Ca²⁺ _(aq)+ 2e-	→ → → → → →	Cu _(s) H₂_(g) Cd _(s) Be _(s) Ca _(s)