1 Chapter 20 Oxidation-Reduction Reactions (Redox Reactions)
Chapter 19: Oxidation-Reduction (Redox) Reactions A clear example of oxidation.
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Transcript of Chapter 19: Oxidation-Reduction (Redox) Reactions A clear example of oxidation.
Chapter 19:
Oxidation-Reduction(Redox)Reactions
A clear example of oxidation
Oxidation and reduction reactions:what the gosh darn heck are they?
Oxidation: the LOSS of electrons
Reduction: the GAIN of electrons
Redox reactions what they mean!!!!1!
LEO the lion says GER! OIL RIG
Loss of Electrons is Oxidation.Gain of Electrons is Reduction.
Oxidation Is Loss of electrons.Reduction Is Gain of electrons.
Connection to Electrochemistry
RED CAT AN OX
REDuction occurs at the CAThode.OXidation occurs at the ANode.
Half Reactions• Show what happens to electrons in the two parts of
a redox reaction: the reduction and the oxidation• Steel hulls in ships have zinc blocks attached
because they oxidize and release electrons. These electrons get consumed by the steel and prevent corrosion.
Rules for Writing Half-Reactions Equations
1. The number of electrons gained must equal
the number of electrons lost.
2. The equation must balance with respect to
both atoms and charge.
(Charge and mass are conserved in redox equations.)
Assigning Oxidation Numbers
Write the half-reaction equations for the redox reaction
Mg (s) + Br2 (l) → MgBr2 (s)
• Step 1: Use oxidation numbers to determine what is oxidized and what is reduced
0 0 2+ 1-
Mg (s) + Br2 (l) → MgBr2 (s)
What happened to Mg?
Mg gained a positive charge so it lost electrons.
It is oxidized.
0 0 2+ 1-
Mg (s) + Br2 (l) → MgBr2 (s)
What happened to Br2?
Br2 got a negative charge so it gained electrons.
It is reduced.
• Step 2 : Write two separate equations: one showing oxidation and another showing reduction. Use coefficients to balance the number of atoms.
Mg → Mg2+
Br2 → 2Br-
Step 3: Make the charge balance in each equation by adding electrons.
Mg → Mg2+ + 2e-
Br2 + 2e- → 2Br-
Check:1. The number of electrons gained must
equal the number of electrons lost.
2. The equation must balance with respect to both atoms and charge.
Redox Reactions and Covalent Bonds
• When hydrogen burns in chlorine, a covalent bond forms from the sharing of two electrons.
• The pair of electrons is more strongly attracted to the chlorine atom because of its higher electronegativity.
2 2
0 0 +1 1
H + Cl 2HCl–
• Neither atom has totally lost or totally gained any electrons.
• Hydrogen has donated a share of its bonding electron to the chlorine but has not completely transferred that electron.
Objectives
• Explain what must be conserved in redox equations.
• Balance redox equations by using the half-reaction method.
• Relate chemical activity to oxidizing and reducing strength.
• Explain the concept of disproportionation.