Topic: Electrochemical Cells - PowerPoint Presentation

Slide1

Topic: Electrochemical Cells

Do Now

: 5 color pencilsSlide2

Electrochemistry

– the study of the relationship between chemical potential energy and electrical energy Slide3

All this occurs Via flow of electrons

Chemical

rxns

can produce electricity

OR

Electrical energy can be used carry out chemical reactions

A Chemical reactions can generate electrical energy if it occurs spontaneouslySlide4

How does a spontaneous reaction generate electricity?

Electrochemical Cells

AKA

voltaic cell or galvanic cell

Used when the chemical

rxn

is spontaneous

It produces electricity (energy) via flow of electrons through a wire therefore is exothermic

Oxidation and Reduction Reaction have to be separatedSlide5

Remember the lab SR lab

AgNO

3

+ Cu

 _______ +_______

Was this spontaneous?

Was this a redox?

So why didn’t we produce electricity?

Ag

CuNO

3

yes

Yes,

Ag was Reduced

& Cu was Oxidized

-2

+5

+1

0

-2

+5

0

+1

Half reactions weren’t separated Slide6

Electrochemical Cell Requirements

2

half-cells

containing

aqueous solution

& an

electrode

Need

to be connected by a wire for the electrons to flow through.Need to be connected by a

salt bridge to maintain electrical neutrality. (if electrons are moving ions need to move also = + ions will flow in same direction as electrons)

Zn

+2

aq

SO

4

-2

aq

Cu

+2

aq

SO

4

-2

aqSlide7

Voltmeter = measures electrical current

When the cells reach

e

quilibrium

voltage = 0 =no more electrical currentSlide8

Electrode

Surface at which oxidation or reduction half-reaction occurs.

Anode – Oxidation

The anode = location for the oxidation half-reaction.

Reduction – Cathode

The cathode = location for the reduction half-reaction.Slide9

MOVIE CLIP

MEMORIZE

Fat

Red

Cat

ate

An

Ox

Anode

oxidation

Fat (getting bigger) Reduction Cathode

yummy

Crap

Slide10

Since Cu is the cathode – a fat red cat = gain mass

Where does the mass come from?

Reduction of Cu

+2

is gaining 2 e

- to make CuSo the concentration of Cu+2

ions decreasesSince Zn is the anode – An ox was eaten = lost e- = getting smaller

Oxidation = Lose electrons, who is going to lose Zn or Zn

+2

Zn

 Zn+2

+ 2e-So the concentration of Zn

+2 increasesSlide11

Is this reaction at equilibrium? How can you tell?

What is happening to the concentration of Zn

+2

ions?

What is happening to the concentration of Cu

+2

ions?

No – volts not a 0

increasing

decreasingSlide12

How do you know which electrode is which?

Use

Table J

to predict which electrode is the anode

/ cathode.

higher in Table J.

gets oxidized

Anode = Oxidation = Electron Donor

lower in Table J

. gets reduced

Cathode = Reduction = Electron AcceptorSlide13

Label anode and cathode

anode

cathodeSlide14

Electrons flow from Anode to Cathode

Cathode is (+) Anode is (-)

Positive Ions flow in same direction as electrons via Salt bridge (too offset the negative electrons)

Which direction would the negative ions flow?

anode

cathode

e

-



e

-



e

-



e

-



e-  e

-

+

 + 

+



+

Anode = site of oxidation

=getting smaller

cathode = site of reduction

=getting largerSlide15

What’s wrong with this picture?

No salt bridge = needed to complete the circuit so ions can flowSlide16

Now you try

Create an galvanic (electrochemical) cell with Al and

Pb

and AlNO

3

and Pb(NO3)2

Label anode and cathode(Use Table J), direction of electron flow in wire, direction of positive ion flow in salt bridge, positive electrode, negative electrode.

Pb

AlSlide17

Pb

Al

Create an galvanic (electrochemical) cell with Al and

Pb

and AlNO

3

and

Pb

(NO

3

)

2

Label anode and cathode(Use Table J), direction of electron flow in wire, direction of positive ion flow in salt bridge, positive electrode, negative electrode.

Al

anode

cathode

e

-



e

-



e

-



e

-



e

-



e

-

Pb

+2

& NO

3

-1

Al+3 & NO3-1Slide18

What

half

-reactions

occured

?

REMEMBER Al got smaller and Pb got bigger

Al  Al+3 + 3

e

-

Pb

+2

+ 2e- 

Pb

Al was the anode, it was oxidized, it lost e

-

Pb

got bigger. How? By gaining electrons. The Pb

+2

ions gained 2 e

-

to make

Pb

.Slide19

Overall Spontaneous Rxn

2(Al

 Al

+3

+ 3

e

-)3(Pb

+2

+ 2

e

-  Pb)

+

_______________________

2Al + 3Pb

+2

 2Al

+3

+ 3PbSlide20

2Al + 3Pb+2

 2Al

+3

+ 3Pb

Which electrode is losing mass?

Which electrode is gaining mass?What’s happening to the [Al

+3

]

?What

’s happening to the [Pb+2]?

Al because now Al

+3

ions in solution

Pb

, Pb

+2

gains 2e

-

an makes solid

Pb

Increasing

DecreasingSlide21

Notation for CellsSlide22

Application: BatteriesSlide23

Dry CellSlide24

Mercury battery