Chemistry12ElectrochemistryII

Name:Date:Block:

1. Half-Reactions2. BalancingRedoxReactions

Half-ReactionsConsiderthefollowingreaction:

Zn(s)+2Cu+(aq)àZn2+(aq)+2Cu(s)

• Noticethat2Cu+ionsarereducedforevery1Znatomoxidized.• Itispossibletoseparateoutthereductionandoxidationportionsofaredoxreaction.• Half-reactions:anequationrepresentingeitheranoxidationorareductionincludingthe

numberofelectronslostorgained.

Oxidation:ZnàZn2++2e-Reduction:Cu++e-àCu

Considerthefollowingreaction:

IO3-+HSO3-àSO42-+I2

Oxidation: Reduction:BalancingHalf-ReactionsSteps:

1.

2.

3.

4.

5.

• Mostreactionsoccurinacidicconditions.However,ifitisstatedthatthereactiontakesplaceinbasicconditions…

6.

Practice:Balancethefollowinghalf-reactions.Alsostatewhetherthisisanoxidationorareduction:

1. ClO4-àCl2

☐ Balancemajoratoms. ☐ BalanceO’s. ☐ BalanceH’s. ☐ Balancecharge.(check!)

2. SmàSm3+

☐ Balancemajoratoms. ☐ BalanceO’s. ☐ BalanceH’s. ☐ Balancecharge.(check!)

3. NO3-àNH4+

☐ Balancemajoratoms. ☐ BalanceO’s. ☐ BalanceH’s. ☐ Balancecharge.(check!)

4. S2O32-àSO42-(basic)

☐ Balancemajoratoms. ☐ BalanceO’s. ☐ BalanceH’s. ☐ Balancecharge.(check!)

HebdenWorkbookPg.203#19

BalancingRedoxReactions:

Rules:

1.

2.

3.

4.

5.

Practice:

IO3-+HSO3-àSO42-+I2

• Separateintotwohalfreactions.(Lookforcommonatomstohelpyou.)

• Balanceeachhalfreaction.(Theremustbeanelectrongaininonesideandlossontheother!)

• Balancetheelectronlossandgain.(checkoxidationnumbers!)

• Addthebalancedhalf-reactionstogether,cancellingwhereappropriate.

H3AsO4+ZnàAsH3+Zn2+

FeHPO3+Cr2O72-àCr3++H3PO4+Fe3+(underbasicconditions)

Adisproportionationreactionisaredoxreactioninwhichthesamespeciesisbothreducedandoxidized.Sincethereisonlyonereactant,thereactantmustbeinvolvedinboththereductionreactionandtheoxidationreaction.

ClO2-àClO3-+Cl-

P4àHPO42-+PH3

HebdenWorkbookPg.207#24Worksheet