Wednesday, April 16, Return Quiz 2.Return Reading Analysis Go over homework 4. Notes Section Homework – Reading Analysis Section 18.2

Redox Reactions 2Na(s) + Cl 2 (g)  2NaCl(s) Assign oxidation states to all elements. What was oxidized? How many electrons were transferred? What was reduced? How many electrons?

Redox Reactions Na is the reducing agent – the reactant that causes something else to be reduced. When identifying, name the entire compound and not just an element. Na is the reducing agent – the reactant that causes something else to be reduced. When identifying, name the entire compound and not just an element. Cl 2 is the oxidizing agent. Cl 2 is the oxidizing agent.

Agents Oxidizing agent also called the electron acceptor Oxidizing agent also called the electron acceptor Reducing reagent is called the electron donor Reducing reagent is called the electron donor

Redox Reactions Oxidation is now defined as an increase in the oxidation state Oxidation is now defined as an increase in the oxidation state Reduction is a decrease in oxidation state Reduction is a decrease in oxidation state

Redox Reactions CH 4 + 2O 2  CO 2 + 2H 2 O Identify the oxidation states of all elements on both sides. Which was oxidized? Reduced? How many e- involved in oxidation? Reduction? What happens to H? What is the oxidizing agent? Reducing agent?

Redox Reactions For each of the following, assign oxidation states, determine what is oxidized and reduced, and what is the oxidizing agent. 2PbS + 3O 2  2PbO + 2SO 2 2PbS + 3O 2  2PbO + 2SO 2 PbO + CO  Pb + CO 2 PbO + CO  Pb + CO 2 N 2 + 3H 2  2NH 3 N 2 + 3H 2  2NH 3

Balancing Redox Reactions Can balance with guess and check… tedious Can balance with guess and check… tedious Use half-reactions: equations that have electrons as reactants or products Use half-reactions: equations that have electrons as reactants or products One half reaction is the oxidation reaction One half reaction is the oxidation reaction The other half reaction is reduction The other half reaction is reduction

Balancing Redox Reactions In the oxidation half reaction the electrons are shown on the product side (lost by the reactant) In the oxidation half reaction the electrons are shown on the product side (lost by the reactant) In the reduction half reaction electrons are shown on the reactant side (electrons are gained by a reactant in the equation) In the reduction half reaction electrons are shown on the reactant side (electrons are gained by a reactant in the equation)

Steps to Balance 1. Separate the reaction into an oxidation half-reaction and a reduction half-reaction 1. Separate the reaction into an oxidation half-reaction and a reduction half-reaction 2. Balance the half reactions separately 2. Balance the half reactions separately 3. Equalize the number of electrons gained and lost 3. Equalize the number of electrons gained and lost 4. Add the half-reactions together and cancel electrons to give the overall balanced equation 4. Add the half-reactions together and cancel electrons to give the overall balanced equation

Redox Reactions Half Reactions Mg  Mg e - Cu e -  Cu The # of e- gained must = the # lost Complete Ionic Equation Mg + Cu e -  Cu + Mg e - Net Ionic Equation Mg + Cu 2+  Cu + Mg 2+

Redox Equations Write the two half reactions when Zn and Fe 3+ were combined. (Zn  Zn e - )3 (Fe e -  Fe)2 Give the complete and net ionic equations. 3Zn + 2Fe e -  2Fe + 3Zn e - 3Zn + 2Fe 3+  2Fe + 3Zn 2+

Redox Equations Write out a half reaction showing what occurs when F 2 gains electrons. F 2 + 2e-  2F - Write out a half reaction for N 2 gaining electrons. N 2 + 6e-  2N 3-

Redox Equations Write the two half reactions when Zn forms Zn 2+ and Ag + forms Ag. Then write the complete and net ionic equations. Zn  Zn e - (Ag + + e -  Ag)2 Zn + 2Ag + + 2e -  2Ag + Zn e - Zn + 2Ag +  2Ag + Zn 2+