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Redox Reactions

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

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  1. Redox Reactions Glenn V. Lo Department of Physical Sciences Nicholls State University

  2. 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

  3. 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

  4. 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+

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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”

  10. 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

  11. Non-redox reactions • Double replacement reactions • Precipitation • AgNO3 + HCl  AgCl + HNO3 • Ag+ + Cl-  AgCl • Acid-Base Neutralization • HCl + NaOH  NaCl + H2O • H+ + OH-  H2O

  12. 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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