2. Redox Reactions

What occurs in a redox reaction?

electrons move from the substance being oxidized to the substance being reduced

What are Half-Reactions?

a chemical equation that represents one part of a redox reaction

• can help show change/ transfer of electrons

• eg. Cu(s) Cu2+ (aq) + 2e-

  Ag+ (aq) + e- Ag (s)

ELECTRONS ARE ADDED TO EITHER SIDE TO BALANCE CHARGES AND THE AMOUNT LOST IN ONE HALF-REACTION MUST BE GAINED IN THE OTHER HALF-REACTION

What is important to remember about electrons in Redox Rxns?

1. electrons are added to either side to balance charges

2. # electrons lost in one reaction must be gained in the other

What are the steps to solving Redox Rxns?

1. Assign oxidation states to determine which atoms are being oxidized and which are being reduced

2. Write half-equations for oxidation and reduction as follows:

   1. balance the atoms other than H and O

   2. balance each half-equation for O by adding H2O

      as needed

   3. balance each half-equation for H by adding H+

      as needed

   4. balance each half-equation for charge by adding

      electrons to the sides with more positive charge

   5. check that each half-equation is balanced for

      atoms and for charge

3. Equalize the number of electrons in the two half-equations by multiplying each appropriately

4. Add the two half-equations together, cancelling out anything that is the same on both sides

Oxidizing Agent

substance that gains electrons (being reduced)

• brings about oxidation of the other reactant

Reducing Agent

substance that is losing electrons (becomes oxidized)

• brings about reduction of the other reactant

Apply the terms of Redox and Agents to the reaction presented:

1. Hydrogen is oxidized

2. Oxygen is reduced

3. H₂ is the reducing agent

4. O₂ is the oxidizing agent.

Whether a species acts as an oxidizing or as a reducing agent depends on…

what it is reacting with

What do relative strengths of agents depend on?

depends on their tendencies to lose or gain electrons

• more reactive metals lose electrons more readily so they are stronger reducing agents)

How can one test relative strengths of Reducing Agents?

see if a metal can reduce ions of another metal in solution

the opposite reaction (Cu kicking Zn off) would not happen as Zn is more reactive

Tell me about the Activity Series

• tool that enables us to predict whether a redox reaction between a metals and the ions of another metal is feasible

• found by testing different displacement reactions together