Monday 2 April 2018

CLASS 10 - CHEMISTRY - CHEMICAL REACTIONS AND EQUATIONS - Chapter Summary Notes (#eduvictors)(#cbsenotes)


Chapter Summary Notes

1. Chemical reaction — 

Chemical changes or chemical reactions are the changes in which one or more new substances are formed.

2. Chemical Equations – 

Representation of a chemical reaction in terms of symbols and formulae of the reactants and products is known as a chemical equation.

3. Balanced Chemical equations – 

The chemical equation in which the no. of atoms of different elements is same on both sides of the arrow is called balanced chemical equation.

4. The chemical reactions can be classified into different types such as—

a. Combination reaction.
b. Decomposition reaction.
c. Displacement reaction.
 d. Double Displacement reaction.
i. Precipitation reaction
ii. Neutralization reaction
e. Redox reaction

5. Combination reaction – 

The reactions in which two or more substances combine to form a new substance are called combination reaction.
For example,

2Mg(s) + O₂ (g) -----→ 2 MgO (s)

6. Decomposition reaction - 

The reaction in which a single compound breaks up into two or more simpler substances are called decomposition reactions. For example,

2Pb(NO₃)₂ (s) -----→ 2PbO (s) + 4NO₂ (g) +O₂ (g)

The decomposition of a substance by passing an electric current through it is known as electrolysis (Electrical Decomposition).
The decomposition of a substance on heating is known as thermal decomposition.
The decomposition of a substance by absorbing light energy is called photochemical decomposition.

7 Displacement reactions -

The chemical reactions in which a more reactive element displaces a less reactive element from a compound are known as displacement
reactions. For example,

Zn (s) + CuSO₄ (aq) -----→ ZnSO₄ (aq) + Cu (s)
Cu (s) + 2AgNO₃ (aq) -----→ Cu(NO₃)₂ (aq) +2Ag(s)

8. Double Displacement Reactions - 

The chemical reactions in which compounds react to form two different compounds by mutual exchange of ions are called double displacement reactions.

These reactions take place in solution two common types of this reaction are precipitation reactions and neutralization reactions

i) Precipitation reaction: In this reactions, an aqueous solution of two salts are mixed whereby some salts precipitate due to the mutual exchange of ions between the two salts.
For example
AgNO₃ (aq) + NaCl (aq) -----> AgCl(s) + NaNO₃

ii) Neutralization reaction: In this type of reaction an acid reacts with a base to form salt and water by exchange of ions.

NaOH (aq) + HCl (aq) -----> NaCl (aq) + H₂O

9. Redox reaction - 

The chemical reaction which shows both oxidation and reduction reaction.

Oxidation: Reaction that involves the gain of oxygen or loss of hydrogen.

Reduction: Reaction that shows the loss of oxygen or gain of hydrogen.

Both oxidation and reduction take place simultaneously and hence called redox reaction.

ZnO + C ------> Zn +CO
ZnO reduce to Zn ---- reduction
C oxidize to CO ------oxidation

10. Exothermic reaction and endothermic reaction

On the basis of energy changes during a chemical reaction, they can be classified as

i. Exothermic reaction: A chemical reaction in which heat energy is produced.
C + O₂ --------> CO₂ (g) + heat

ii. Endothermic reaction: A chemical reaction in which heat energy is absorbed.
CaCO₃ + Heat -------> CaO + CO₂

11. Corrosion – 

The process of slow conversion of metals into their undesirable compounds due to their reaction with oxygen, water, acids, gases etc. present in the atmosphere is called corrosion.

Rusting – Iron when reacts with oxygen and moisture forms a red substance called rust. The chemical composition of rust is Fe₂O₃.xH₂O. Its chemical name is Hydrated Iron (III) oxide.

12. Rancidity – 

The taste and odour of food materials containing fat and oil changes when they are left exposed to air for a long time. This is called rancidity. It is caused due to oxidation of fat and oil present in the food material.

It can be prevented by using various methods such as by adding antioxidants to the food materials. Storing food in an airtight container and by flushing out air with nitrogen.

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