Electrochemistry-Review on Redox Reaction and Balancing a Redox Reaction

8/8/2019 Electrochemistry-Review on Redox Reaction and Balancing a Redox Reaction

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LOVELY PROFESSIONALLOVELY PROFESSIONAL

UNIVERSITYUNIVERSITY


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TERM PAPER OF CHEMISTRY

TOPIC-

ELECTROCHEMISTRY-REVIEW ON REDOX

REACTIONS

AND BALANCING REDOX

REACTIONS.


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ACKNOWLEDGEMENT

I take this opportunity to present my votes ofthanks to all those guidepost who really actedas lightening pillars to enlighten our way

throughout this project that has led tosuccessful and satisfactory completion of thisstudy.

I am thankful to my teacher Ms. GAGANDEEPKAUR to be active and helpful enough to make

me complete this term paper.

RAHUL SINHA


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ELECTROCHEMISTRY-REVIEW ON

REDOX REACTIONS

AND BALANCING REDOX REACTIONS.

CONTENTS- OXIDATION.

REDUCTION. DEFINATION OF REDOX REACTION.

RULES FOR OXIDATION STATE.

TYPES OF REDOX REACTIONS.

HALF CELL REACTIONS.

BALANCING A REDOX REACTION.

BALANCING IN ACIDIC AND BASIC MEDIUM.


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Oxidation/Reduction

ReactionsAcid/Base reactions

involve a donation /acceptance of protons

Precipitation/ Solubility reactions

involve a donation/ acceptance of negative

charge

what is being donated and accepted in a

redox reaction?


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Oxidation/Reduction

Reactions Electrons!

Consider the reaction taking place in a

disposable battery:

2Zn + 3MnO2 p Mn3O4 + 2ZnO

How can you tell that electrons are beingdonated and accepted? Which species isdonating electron( s) and which is acceptingelectron (s)?


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Redox reactions are characterized byRedox reactions are characterized by

ELECTRON TRANSFERELECTRON TRANSFER between anbetween an

electron donor and electron acceptor.electron donor and electron acceptor.

REDOX REACTIONSREDOX REACTIONS


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Transfer leads toTransfer leads to

1.1. increase in oxidation numberincrease in oxidation numberofof

some element =some element = OXIDATIONOXIDATION

2.2. decrease in oxidation numberdecrease in oxidation numberofof

some element =some element = REDUCTIONREDUCTION

REDOX REACTIONSREDOX REACTIONS


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Electron Transfer in Redox

Reactions Oxidation

Loss of electrons

Gain in oxygen

Reduction

Gain of electrons Loss of oxygen

LEO the lion goes Ger


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Example

The reaction of a metal and non-metal

All the electrons must be accounted for!

Mg S+ Mg 2+ + S2-


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Oxidation-Reduction

Oxidation means an increase in oxidation state - lose

electrons.

Reduction means a decrease in oxidation state - gain

electrons.

The substance that is oxidized is called the reducingagent.

The substance that is reduced is called the oxidizing

agent.


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Assigning Oxidation States

An Oxidation-reduction reaction

involves the transfer of electrons.

Oxidation No. of an atom is zero.


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Rules for Oxidation States

The charge the atom would have in a molecule

(or an ionic compound) if electrons were

completely transferred.

The oxidation state of elements in their

standard states is zero.

Example: Na, Be, K, Pb, H2, O2, P4 = 0


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Assigning Oxidation States Oxidation state for monatomic ions are the same as

their charge.

Example: Li+, Li = +1; Fe3+, Fe = +3; O2-, O = -2

Oxygen is assigned an oxidation state of -2 in its

covalent compounds except as a peroxide.


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Rules for Oxidation States

4. The oxidation number of hydrogen is +1

exceptwhen it is bonded to metals in binary

compounds. In these cases, its oxidation

number is1.

5. Group IA metals are +1, IIA metals are +2 and

fluorine is always1.

6. The sum of the oxidation numbers of all the

atoms in a molecule or ion is equal to the

charge on the molecule or ion.


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Identify the

Oxidizing agent-Substance which is reduced

itself and oxidize others is called Oxidizing Agent

Reducing agent-Substance which oxidize itself

and reduce others is called Reducing Agent

Substance oxidized-The substance whose

oxidation no. increases is called substance

oxidised.

Substance reduced- The substance whose

oxidation no. is reduced is called substance

reduced.


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Types of Oxidation-Reduction Reactions

Combination Reaction

A + B C

S + O2 SO2

Decomposition Reaction

2KClO3 2KCl + 3O2

C A + B

0 0 +4 -2

+1 +5 -2 +1 -1 0


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Displacement Reaction a.k.a Single Replacement

A + BC AC + B

Sr + 2H2O Sr(OH)2 + H2

TiCl4 + 2Mg Ti + 2MgCl2

Cl2 + 2KBr 2KCl + Br2

Hydrogen Displacement

Metal Displacement

Halogen Displacement


0 +1 +2 0

0+4 0 +2

0 -1 -1 0


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The Activity Series for Metals

M + BC AC + B

Hydrogen Displacement Reaction

M is metalBC is acid or H2O

B is H2

Ca + 2H2O Ca(OH)2 + H2


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Disproportionation Reaction

Cl2 + 2OH-

ClO-

+ Cl-

+ H2O

Element is simultaneously oxidized and reduced.


Chlorine Chemistry

0 +1 -1


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Half-Reactions

All redox reactions can be thought of as

happening in two halves.

One produces electrons - Oxidation half.

The other requires electrons - Reduction

half.


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Half-Reactions

Write the half reactions for the following.

Na + Cl2 Na+ + Cl-

SO3- + H+ + MnO4

- SO4- + H2O + Mn+2


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Balancing Redox Equations

Write separate half reactions

For each half reaction balance all

reactants except H and O

Balance O using H2O


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Acidic Solution

Balance H using H+

Balance charge using e-


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Acidic Solution

Multiply equations to make electrons

equal

Add equations and cancel identical

species

Check that charges and elements are

balanced.


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Basic Solution

Do everything you would with acid, but add

one more step.

Add enough OH- to both sides to neutralize

the H+

CrI3 + Cl2 p CrO4- + IO4

- + Cl-

CN- + MnO4- CNO- + MnO2


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BIBLIOGRAPHY

N.C.E.R.T BOOK .

RAYMOND AND CHANG.

GOOGLE SEARCH.

Ms. GAGANDEEP KAUR.

ANDWIKIPEDIA ENCYCLOPEDIA.


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THANK YOU

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Electrochemistry-Review on Redox Reaction and Balancing a Redox Reaction

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