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Redox Reactions
Glenn V. LoDepartment of Physical SciencesNicholls State University
What is a redox reaction?
Redox is short for Reduction-Oxidation.Reduction: gain of electronsOxidation: loss of electronsA redox reaction is an “electron transfer” reaction
Reduction or Oxidation?
State if the following is a reduction or oxidation? F2 molecule becomes two fluoride ions O + 2e- O2-
Na Na+ + e-
Mg atom becomes Mg2+ ion
Oxidation: more positive chargeReduction: more negative charge
Half or Full?
Reduction and oxidation are “half reactions.” If something is reduced, something else is oxidized.Chemical equation for a redox reaction should reflect the fact that the following are equal: Number of electrons lost in oxidation half Number of electrons gained in reduction half
Why is the following considered unbalanced? Ag+ + Cu Ag + Cu2+
Recognizing Redox Reactions
You should be able to recognize reactions involving an elemental substance as redox reactionsNot all redox reactions involve an elemental form of a substance
Combination Reactions
Reactions involving an elemental substance are redox reactionsExample: combination of two elements to form a compound 2 Na + Cl2 2 NaCl Na is oxidized to Na+ ion Cl2 is reduced to two Cl- ions
Displacement Reactions
Reactions involving an elemental substance are redox reactionsExample: displacement of an element in one compound by another 2 Na + 2 HOH 2 NaOH + H2
Na is oxidized to Na+ ion What’s reduced?
Also called “single replacement”Application: extraction of precious metals
Combustion Reactions
Reactions involving an elemental substance are redox reactionsExample: combustion reactions (reaction with O2, leading to formation of oxides) Mg + 2 O2 2 MgO (also
combination) CH4 + 2 O2 2 CO2 + 2 H2O
Electron transfer?
How could there be electron transfer in CH4 + 2 O2 2 CO2 + 2 H2O
In molecules, atoms are sharing electrons.However, sharing is generally not “equal”. In CO2, electrons shared between C and O are “polarized towards O.” In O2, electrons are equal shared (why?)From O2 to CO2, O atoms may be thought of as having “gained electrons”
Decomposition
Decomposition reactions involve the breakdown of ONE reactant into two or more products.If one of the decomposition products is an element, the reaction is redox. Ex. 2 H2O 2 H2 + O2
Non-redox reactions
Double replacement reactionsPrecipitation AgNO3 + HCl AgCl + HNO3
Ag+ + Cl- AgCl
Acid-Base Neutralization HCl + NaOH NaCl + H2O H+ + OH- H2O
Non-redox reactions
Combination of two compounds to form another compound CaO + H2O Ca(OH)2
Decomposition, when none of the products is an elemental substance. CaCO3 CaO + CO2
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