Chapter 19 Redox Reactions

Oxidation Numbers Rules Examples Uncombined element = 0 Monatomic ion = charge on ion (from location of periodic table) 2 element compound – right gets what it wants (from periodic table), calculate left 3 element compound – right and left get what they want, calculate middle Examples

Oxidation-Reduction (Redox) Loss of e- (becomes more positive) Reduction Gain of e- (becomes more negative) LEO the lion says GER Loss of e- is oxidation Gain of e- is reduction Example

Recognizing Redox Reactions THERE HAS TO BE A CHANGE IN OXIDATION NUMBER FOR A REACTION TO BE REDOX!! Examples

Half-Reactions Separate redox reaction into the individual oxidation and reduction reactions Examples

Redox Reactions Oxidizing Agent Reducing Agent Substance that causes oxidation It is Reduced! Reducing Agent Substance that causes reduction It is Oxidized!

Balancing Half-Reactions Steps: Write half-reactions separately Balance everything except H and O Balance O by adding water Balance H by adding H+ Balance overall charge by adding e-’s Add oxidation and reduction reactions with equal e-’s Cancel if possible

Balancing Half-Reactions Examples

Electrochemistry Using half-reactions and calculating voltages Anode Site of oxidation Lower reduction potential Cathode Site of reduction Ecell = Ecathode – Eanode

Electrochemistry Examples Cr+3+/Cr with Zn+2/Zn – Use chart on page 615

Calculating Voltage for a Cell Zn2+/Zn with Cu2+/Cu What two half reactions will occur? What is the oxidation half reaction? What is the reduction half reaction? What would the voltage reading be for the entire cell? Which electrode would get bigger? Which electrode would be consumed?

Calculating Voltage for a Cell