Regents Warm-Up

Given the balanced equation representing a reaction: Cl 2 (g)  Cl(g) + Cl(g) What occurs during this change?

(1) Energy is absorbed and a bond is broken.

(2) Energy is absorbed and a bond is formed.

(3) Energy is released and a bond is broken.

(4) Energy is released and a bond is formed.

Electrochemistry

AIM: What is a Voltaic Cell?

Do Now: In the rxn: 2Mg + O 2  2MgO What is oxidized & what is reduced?

Electrochemistry

• Electrochemistry: is the study of the relationship between electrical energy and chemical reactions • In redox reactions electrons are transferred between 2 atoms Example Zn 0 + Cu +2  Zn +2 + Cu 0 • This is a spontaneous rxn • What is oxidized & what is reduced?

• There are 2 types of electrochemical cells

Voltaic Cell

• Voltaic Cell: uses a spontaneous redox reaction to provide a source of electricity • Oxidation-Reduction half reactions take place in different containers called half cells • Half-cells are connected by what is called a salt bridge • What’s an everyday example of a voltaic cell?

• Batteries are voltaic cells

Voltaic Cell

• Oxidation occurs in the left half-cell • This is where electrons are lost • They travel through the connected electrodes into the reduction half cell • This flow of electrons is electricity

Voltaic Cell

• The solid metal strips are called electrodes • The electrode where O XIDATION takes place is the A NODE • The electrode where R EDUCTION takes place is the C ATHODE • Electrons ALWAYS flow from the anode to the cathode

Voltaic Cell

• There will be a connection between the 2 half-cells where ions can flow to balance the flow of electrons • If the wire connecting the electrodes is connected to an external circuit, the cell is a source of electrical energy

Voltaic Cell

• In a battery the anode is the negative terminal • The cathode is the positive terminal Why does a battery “die”?

Voltaic cells

• After awhile the redox reaction come to equilibrium and the cell(battery) no longer operates

Voltaic Cells • Cathode



Reduction (both start w/consonants) • Anode



Oxidation (both start w/ vowels)

Voltaic Cells

A voltaic cell spontaneously converts Which energy conversion occurs during the operation of a voltaic cell?

1.

electrical energy to chemical energy

2.

electrical energy to nuclear energy

3.

chemical energy to electrical energy

4.

nuclear energy to electrical energy

1.

Chemical energy is spontaneously converted to electrical energy.

2.

Electrical energy is spontaneously converted to chemical energy.

3.

Chemical energy is converted to electrical energy only when an external power source is provided.

4.

Electrical energy is converted to chemical energy only when an external power source is provided.

Voltaic Cells

What is the purpose of the salt bridge in a voltaic cell?

In a voltaic cell, chemical energy is converted to

1.

It blocks the flow of electrons.

2.

It is a path for the flow of electrons.

3.

It blocks the flow of positive and negative ions.

4.

It is a path for the flow of positive and negative ions.

1.

electrical energy, spontaneously

2.

nuclear energy, spontaneously

3.

electrical energy, nonspontaneously

4.

nuclear energy, nonspontaneously

Voltaic Cells

Given the balanced equation representing the reaction occurring in a voltaic cell: Zn(s) + Pb 2+ (aq) → Zn 2+ (aq) + Pb(s) In the completed external circuit, the electrons flow from

1.

Pb(s) to Zn(s)

2.

Zn(s) to Pb(s)

3.

Pb 2+ (aq) to Zn 2+ (aq)

4.

Zn 2+ (aq) to Pb 2+ (aq)