Ch 19: Electrochemistry

Define a redox reaction

a reaction in which there are changes in oxidation states

• ex.) Sn(s) + Cu²⁺ to Cu (s) + Sn²⁺(aq)

• Sn=0 and Cu=+2 to Cu=0 and Sn=+2

What are the steps when using the half-reaction method to balance a redox reaction?

1. separate unbalanced reaction into half reactions

2. balance each half-reaction with regard to atoms other than O and H

3. Balance O by adding H2O

4. Balance H by adding H+

5. Balance charge by adding electrons

6. Multiply as necessary so number of electrons for in half-reactions are equal

7. add half-reactions together and cancel electrons

8. For each H+ ion, add 1 OH- to both sides of the equation

9. Make any additional cancellations made necessary by the new H2O added

   1. ****Steps 8 and 9 are only necessary if reaction is occuring in a basic solution

What does oxidation mean? Reduction?

Oxidation

Is

Lost

Reduction

Is

Gain

Define galvanic cells

an electrochemical generating apparatus that uses a spontaneous reaction to do that

Do electrical currents flow from anode or cathode or cathode to anode?

from anode to cathode because there is a difference in electrical potential energy between the electrodes

What is an anode?

the positively charged electrode by which the electrons leave an electrical device.

Define cathode

the negatively charged electrode by which electrons enter an electrical device

Define cell potential

The electrical potential measured by a voltmeter