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Redox Reactions. Glenn V. Lo Department of Physical Sciences Nicholls State University. What is a redox reaction?. Red ox is short for Red uction- Ox idation. Reduction: gain of electrons Oxidation: loss of electrons A redox reaction is an “electron transfer” reaction.

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redox reactions

Redox Reactions

Glenn V. Lo

Department of Physical Sciences

Nicholls State University

what is a redox reaction
What is a redox reaction?
  • Redox is short for Reduction-Oxidation.
  • Reduction: gain of electrons
  • Oxidation: loss of electrons
  • A redox reaction is an “electron transfer” reaction
reduction or oxidation
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 charge
  • Reduction: more negative charge
half or full
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
Recognizing Redox Reactions
  • You should be able to recognize reactions involving an elemental substance as redox reactions
  • Not all redox reactions involve an elemental form of a substance
combination reactions
Combination Reactions
  • Reactions involving an elemental substance are redox reactions
  • Example: 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
Displacement Reactions
  • Reactions involving an elemental substance are redox reactions
  • Example: 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
Combustion Reactions
  • Reactions involving an elemental substance are redox reactions
  • Example: 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
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
  • 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
Non-redox reactions
  • Double replacement reactions
  • Precipitation
    • AgNO3 + HCl  AgCl + HNO3
    • Ag+ + Cl-  AgCl
  • Acid-Base Neutralization
    • HCl + NaOH  NaCl + H2O
    • H+ + OH-  H2O
non redox reactions1
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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