Electrochemistry Lesson 3 Spontaneous Reactions. Predicting Spontaneous Reactions Using the Standard Reduction Chart Does Au 3+ react with Cl - ?

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Presentation transcript:

Electrochemistry Lesson 3 Spontaneous Reactions

Predicting Spontaneous Reactions Using the Standard Reduction Chart Does Au 3+ react with Cl - ?

Predicting Spontaneous Reactions Using the Standard Reduction Chart If two half-cells are joined, the higher half- reaction on the table undergoes reduction, while the lower half-reaction undergoes oxidation

Possible situations… If both reactants are found on the left, or both are found on the right, NO reaction will occur ( non spontaneous) Same side  NO reaction

nonspontaneous- both on same side Does Au 3+ react with Fe 3+ ?

Possible situations… If one reactant is found on the left, one is found on the right, a spontaneous reaction will occur if and only if… The reactant on the left side(to be reduced) is ABOVE the reactant on the right side( to be oxidized)

Predicting Spontaneous Reactions Using the Standard Reduction Chart Does Au 3+ react with Cl - ? If it does, write the spontaneous reaction.

The top reaction is written forward- reduction The bottom reaction is written in reverse- oxidation (Au e -  Au (s) ) (2Cl -  Cl 2(g) +2e - ) 2 3 2Au Cl -  3Cl 2(g) + 2Au (s)

spontaneous- downhill Does Fe 3+ react with Pb?

Does Ag + react with Br - ?

nonspontaneous

Some ions are on both sides of the table and are oxidizing or reducing agents. For example: Fe  Fe 2+  Fe 3+ Sn  Sn 2+  Sn 4+ Cu  Cu +  Cu 2+

Does Sn 2+ react with Cr?

spontaneous Check both (Sn e -  Sn (s) ) (Cr (s)  Cr e - ) 3 2 2Cr (s) + 3Sn 2+  2Cr Sn (s)

Can you keep HCl in a Cu container? Explain!

nonspontaneous

Can you keep HCl in a Cu container? Explain! Yes, nonspontaneous. H + is a weaker oxidizing agent than Cu 2+ and Cu +.

Can you keep HCl in a Zn container? Explain!

Spontaneous- no H + is a stronger oxidizing agent than Zn 2+

Write the spontaneous reaction. 2H + + 2e -  H 2(g) Zn (s)  Zn e - 2H + + Zn (s)  H 2(g) +Zn 2+

Can you keep HNO 3 in a Au container? Explain!

Yes, nonspontaneous. HNO 3 is a weaker oxidizing agent than Au 3+.

TRY: Can you keep HNO 3 in a Cu container? Explain!

Take the strongest ox agent- higher Take the strongest red agent- lower

Can you keep HNO 3 in a Cu container? No, spontaneous. HNO 3 is a stronger oxidizing agent than Cu 2+. Write the spontaneous reaction. NO H + + 3e -  NO (g) + 2H 2 Ox2 Cu (s)  Cu e - x3 2NO H + + 3Cu (s)  2NO (g) + 4H 2 O + 3Cu 2+

Homework Hebden: pg. 199 #7-12 (odd); pg