Redox reactions
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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

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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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