Unit 5 ELECTROCHEMISTRY. REDOX REACTIONS OXIDATION: _____________________ REDUCTION: ____________________ REDOX: _____________________________

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Text of Unit 5 ELECTROCHEMISTRY. REDOX REACTIONS OXIDATION: _____________________ REDUCTION:...

Unit 5

Unit 5ELECTROCHEMISTRYREDOX REACTIONSOXIDATION: _____________________REDUCTION: ____________________REDOX: _____________________________EXAMPLE

SHOW, WITH ARROWS, THE LOSS AND GAINS OF ELECTRONSOXIDIZING AGENT: ___________________REDUCING AGENT: ____________________

PRACTICE PROBLEMS, PAGE 467, #1-4

HALF REACTIONSOxidation and reduction can be represented in separate equations. HALF REACTION: BALACEND EQUATION THAT SHOWS THE NUMBER OF ELECTRONS INVOLVED IN EITHER OXIDATION OR REDUCTION.Example...

Half-Reactions are balanced using the smallest possible whole-number coefficientsExample:Is this a proper half reaction?

Disproportionation ReactionsA single element undergoes both oxidation and reduction in the same reaction.

Example:

Practice Problems, 5-8Section ReviewSR: 1-510.2 Oxidation NumbersWe have seen net ionic equations with monatomic elements (Cu, Zn) and single-element ions. We used ionic charges to describe the transfer of electrons.Many reactions involve reactants or products with covalent bonds cannot use ionic charges to describe the transfer of electrons. Oxidation numbers: actual/hypothetical charges, assigned using a set of rules.Describe redox reactions with covalent reactants or products.Oxidation Numbers from Lewis StructuresTo assign oxidation numbers:Consider all bonding electrons be be owned by the more electronegative oxygen atom. H+ has oxidation number +1Oxygen has a filled octet, so -2. THESE ARE NOT IONIC CHARGES!In ionic charges, (-) or (+) written AFTER the value

Molecules with Atoms of Equal ElectronegativityEx// Cl2 : both atoms equally electronegative. Oxidation numbers: 0 for both.

Molecules with Atoms of Different ElectronegativityEx// for CN-,Oxidation number for C: +2Oxidation number for N: -3Oxidation Number RulesOxidation # of:H: +1 except when with metal hydrides: -1O: -2 except peroxides and the OF2 compound.Compounds w/o H or O: same as ionic charge.

Average Oxidation NumbersOxidation numbers are not always integers.Example: Fe3O4 The sum of oxidation numbers for the oxygen atoms will be -8.In order for the compound to be neutral, each iron atom would have to have an oxidation number of +3/8.

Hints:Use the oxidation number rules (obviously!)- These take precedence.Use a variable (x) to figure out the unknown oxidation number.

CHECK PAGE 477 FOR ANSWERS.CARRY OUT PPs 9-11, 12a&b ON PAGE 478.

Applying Oxidation Numbers to Redox ReactionsDetermine the oxidation numbers of the elements within the following reaction.

TO DO SO...Determine the ionic equation (dissociate)Eliminate any spectator ions to get the net ionic equationLook at the net ionic equation and figure out the oxidation numbers for all of the reactants and products.

Redox reactions can also be described as...Oxidation: a(n) ___________________ in oxidation number.Reduction: a(n) ________________ in oxidation number.Hints: oxidizing/reducing agents are REACTANT MOLECULES!If compounds are ionic and aqueous, dissociate!

COMPLETE: PPs #13-15, page 480.SR: 1-6.

10.3: The Half-Reaction Method for Balancing EquationsWe have learned how to divide balanced equations into separate reduction and oxidation reactions.We will now learn how to combine half-reactions into balanced equations.

REVERSE!Formation Reaction of potassium chloride:

Half reactions of this reaction:

Are the atoms and charges balanced?Balancing half-reactions in is more complicated when in acidic or basic solutions.- H+ and OH- need to be taken into account.Balancing Half-Reactions for Acidic Solutions

COMPLETE PPs 17-20.

Balancing Half-Reactions for Basic Solutions

COMPLETE PPs 21-24.

Half-Reaction Method for Balancing Redox ReactionsAdding two half reactions results in an ionic equation.No electrons are created or destroyed in a redox reaction.Add two half-reactions so that the number of electrons lost in oxidation equals the number of electrons gained through reduction. Example:Mg(s) + Al(NO3)3Original Half-reactions:

Multiply half-reactions:

Add results:Eliminate electrons:Include spectator Ions:

Steps for Balancing by the Half-Reaction Method

Half-Reaction Method for Balancing Redox EquationsPPs, page 491. #25-28.SRs, #1-2, 5, 6.

10.4 Oxidation Number Method for Balancing EquationsWhen using the oxidation numbers to balance a chemical equation:The total increase in the oxidation numbers of the oxidized element(s) equals the total decrease in oxidation numbers of the reduced element(s).

Oxidation number of nitrogen increases from -3 to +4, therefore increasing by 7. The oxidation number of oxygen decreases from 0 to -2, a decrease of 2. Two nitrogen atoms must react for every seven oxygen atoms so that the total increase and decrease in oxygen numbers are both 14.

PPs, page 496 #29-32SR, #s 1-4

Chapter 10 ReviewPage 499#s 1-7, 9-10, 12