Chapter 19 Redox Reactions

Oxidation Numbers Rules 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 left Examples

Oxidation-Reduction (Redox) Oxidation Loss of e - (becomes more positive) Ex: Zn -> Zn +2 +2e- Reduction Gain of e - (becomes more negative) Ex: F 2 +2e- -> 2F - LEO the lion says GER Loss of e - is oxidation Gain of e - is reduction Example 2H 2 + O 2 -> 2H 2 O

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 Mg + O 2 -> MgO

Redox Reactions Oxidizing 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 Cathode Site of reduction Use the REDUCTION POTENTIAL CHARTS and ONE will FLIP to make the MOST POSITIVE TOTAL MULTIPLYING BY COEFFICIENT DOES NOT CHANGE VOLTAGE

Electrochemistry Examples

Calculating Voltage for a Cell

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?