Redox Reaction • one or more elements change oxidation number all single displacement, and combustion, some synthesis and decomposition • always have both oxidation and reduction spli
Trang 1Redox Reaction
Trang 2Redox Reaction
• one or more elements change oxidation number
all single displacement, and combustion,
some synthesis and decomposition
• always have both oxidation and reduction
split reaction into oxidation half-reaction and a
reduction half-reaction
• aka electron transfer reactions
half-reactions include electrons
• oxidizing agent is reactant molecule that causes oxidation
contains element reduced
• reducing agent is reactant molecule that causes reduction
contains the element oxidized
Trang 3Oxidation & Reduction
• oxidation is the process that occurs when
oxidation number of an element increases
element loses electrons
compound adds oxygen
compound loses hydrogen
half-reaction has electrons as products
• reduction is the process that occurs when
oxidation number of an element decreases
element gains electrons
compound loses oxygen
compound gains hydrogen
half-reactions have electrons as reactants
Trang 4Rules for Assigning Oxidation States
• rules are in order of priority
1 free elements have an oxidation state = 0
Na = 0 and Cl2 = 0 in 2 Na(s) + Cl2(g)
2 monatomic ions have an oxidation state equal
to their charge
Na = +1 and Cl = -1 in NaCl
3 (a) the sum of the oxidation states of all the
atoms in a compound is 0
Na = +1 and Cl = -1 in NaCl, (+1) + (-1) = 0
Trang 5Rules for Assigning Oxidation States
3. (b) the sum of the oxidation states of all the atoms in
a polyatomic ion equals the charge on the ion
N = +5 and O = -2 in NO3– , (+5) + 3(-2) = -1
4. (a) Group I metals have an oxidation state of +1 in all
their compounds
Na = +1 in NaCl
4. (b) Group II metals have an oxidation state of +2 in
all their compounds
Mg = +2 in MgCl2
Trang 6Rules for Assigning Oxidation States
5 in their compounds, nonmetals have oxidation
states according to the table below
nonmetals higher on the table take priority
Nonmetal Oxidation State Example
Trang 7Oxidation and Reduction
• oxidation occurs when an atom’s oxidation state increases during a reaction
• reduction occurs when an atom’s oxidation state decreases during a reaction
CH4 + 2 O2 → CO2 + 2 H2O
-4 +1 0 +4 –2 +1 -2
oxidation
reduction
Trang 8Oxidation–Reduction
• oxidation and reduction must occur simultaneously
if an atom loses electrons another atom must take them
• the reactant that reduces an element in another reactant
is called the reducing agent
the reducing agent contains the element that is oxidized
• the reactant that oxidizes an element in another reactant
is called the oxidizing agent
the oxidizing agent contains the element that is reduced
2 Na(s) + Cl2(g) → 2 Na+Cl–(s)
Na is oxidized, Cl is reduced
Na is the reducing agent, Cl2 is the oxidizing agent
Trang 9Identify the Oxidizing and Reducing Agents
in Each of the Following
3 H2S + 2 NO3– + 2 H+ 3 S + 2 NO + 4 H2O
MnO2 + 4 HBr MnBr2 + Br2 + 2 H2O
Trang 10Identify the Oxidizing and Reducing Agents
in Each of the Following
3 H2S + 2 NO3– + 2 H+ 3 S + 2 NO + 4 H2O
MnO2 + 4 HBr MnBr2 + Br2 + 2 H2O
+1 -2 +5 -2 +1 0 +2 -2 +1 -2
ox ag
red ag
+4 -2 +1 -1 +2 -1 0 +1 -2
oxidation
reduction
oxidation
reduction
red ag
ox ag