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Chemistry (1st): The redox reaction

COURSE

A couple oxidative-reductive , denoted as oxidant / reductant, is composed of two chemical species combined:

- a oxidant capable capture of electrons (undergoing reduction)

- a gear, capable of donating electrons (suffering oxidation).

Each pair is a half- redox equation: Half equation redox couple of Ox / Red.

couples are classified according to their redox potential , rated E ⁰ in volts (V), defined in relative terms, compared with that of the couple H + / H 2 . Examples of couples oxidative / reductive classified according to their redox potential (P = 1013 hPa and T = 25 ° C).

The redox reaction is a transfer of electrons between two chemical species belonging to two different couples.

The oxidizing couple whose redox potential is highest reacts with the reducing of the couple whose potential is lowest, according to the rule of gamma :

METHOD

Balance redox half equations:

1) Balance the atoms other than O and H.

2) Balance the oxygen atoms of O with H 2 O.

3) Balancing the hydrogen atoms H with H + (in acid).

4) Balance charge with electrons e-.

Example 1: half equation ^{couple Cu 2 +} / Cu
1) OK (1 copper atom Cu per side)
2) OK (no oxygen atom O)
3) OK (no hydrogen atom H)
4) Balance of charges:
Example 2: half equation torque BrO 3 ^- / Br 2

1) Balance of bromine atoms Br:
2) Balance oxygen atoms of O with H 2 O:
3) Balance the hydrogen atoms H with H + :
4) Balance charge with electrons e- :
equation for a redox reaction:

1) Identify the reagents under the rule of gamma.

2) Write half-equations for the two couples involved in the reaction.

3) Balance the given number of electrons and electrons trapped.

4) Add-to-one, then simplify if necessary.

Example: reaction between the couple MnO 4 ^- / Mn 2 + (E 0 = 1.51 V) and the couple I 2 / I ^- (E = 0 0.62 V)

1) Identify reagents:
2) Write the half equations:
3) Balance the number of electrons transferred:
4) Balance: