ElectrochemistryElectrochemistry

CuSO4(aq)

Zn

ZnSO4(aq)

Zn

Cu

ElectrochemistryElectrochemistry

BatteryBattery – uses the energy from a – uses the energy from a redox reaction to produce an redox reaction to produce an electric current and do work.electric current and do work.

ElectrochemistryElectrochemistry – the study of – the study of the interchange of chemical and the interchange of chemical and electrical energy.electrical energy.

ElectrochemistryElectrochemistry

2 Types of electrochemical processes2 Types of electrochemical processes1.1. The production of an electric The production of an electric

current from a chemical (redox) current from a chemical (redox) reaction – battery, voltaic cell, reaction – battery, voltaic cell, galvanic cell.galvanic cell.

2.2. The use of an electrical current to The use of an electrical current to produce a chemical change (redox produce a chemical change (redox reaction). Call this electrolysis.reaction). Call this electrolysis.

ElectrochemistryElectrochemistry

How do we capture the energy?How do we capture the energy? Separate the oxidizing agent Separate the oxidizing agent

(electron acceptor) from the (electron acceptor) from the reducing agent (electron donor)reducing agent (electron donor)

Requires the electron transfer to Requires the electron transfer to occur through a wire or an occur through a wire or an electric motor! electric motor!

Figure 18.1: Schematic for separating the Figure 18.1: Schematic for separating the oxidizing and reducing agents in a redox oxidizing and reducing agents in a redox reaction.reaction.

8H+ + MnO4- + 5e- Mn2+ + 4H20 ; Fe2+ Fe3+ + e-

Why is thereno flow ofelectrons here?

Figure 18.2: Electron Figure 18.2: Electron flow.flow.

8H+ + MnO4- + 5e- Mn2+ + 4H20 ; Fe2+ Fe3+ + e-

Build up of chargeswould require largeamounts of energy

Solutions mustbe connectedto allow ionsto flow

Figure 18.4: The salt Figure 18.4: The salt bridge contains a strong bridge contains a strong electrolyte.electrolyte.

Figure 18.4: The porous disk allows ion flow.

ElectrochemistryElectrochemistry

Want to allow ions to flow but not Want to allow ions to flow but not mix the solutionsmix the solutions

Electrons flow in the wire from Electrons flow in the wire from reducing agent to oxidizing agentreducing agent to oxidizing agent

Electrochemical Electrochemical battery (galvanic cell) battery (galvanic cell) A device powered by a redox A device powered by a redox

reactions where the oxidizing reactions where the oxidizing agent is separated from the agent is separated from the reducing agent so that the reducing agent so that the electrons must travel through a electrons must travel through a wire from reducing agent to wire from reducing agent to oxidizing agentoxidizing agent

Electrochemical Electrochemical battery (galvanic cell) battery (galvanic cell) Reducing agent loses electrons so Reducing agent loses electrons so

it is oxidizedit is oxidized Electrode where oxidation occurs Electrode where oxidation occurs

is called the anodeis called the anode Oxidizing agent gains electrons Oxidizing agent gains electrons

and is reducedand is reduced Electrode where reduction occurs Electrode where reduction occurs

is the cathodeis the cathode

Figure 18.5: Schematic of a Figure 18.5: Schematic of a battery.battery.

Electron flow anode to cathode

oxidation to reduction

Anode - electrode where oxidation occurs

Cathode – electrode where reduction occurs

ElectrochemistryElectrochemistry

Go back to first cell with Zn and Cu and draw a voltaic cell. Label anode, cathode, and show direction of e- flow. Write out the two half reactions and then write out the complete reaction.

Cu/Zn Voltaic CellCu/Zn Voltaic Cell

CuCu2+2+ + 2e- + 2e- Cu Cu Cathode/reductionCathode/reduction

Zn Zn Zn Zn2+ 2+ + 2e- + 2e- Anode/oxidationAnode/oxidation

CuCu2+2+ + Zn + Zn Zn Zn2+ 2+ + Cu+ Cu

Zn2+Cu2+

ZnCu

SO42-

Zn2

+

ElectrochemistryElectrochemistry