presentation on chemical reactions and equations by - Aryan dhiman.pdf

Chemical reactions and equations

1. Chemical Equations
and
Reactions
Class 10 Chemistry
PRESENTATION by - Aryan dhiman

2. Chemica? Reactio?
A chemical reaction is a change in which one or more substances or reactants react to
form a new substance with entirely different properties.
Reacting species are known as reactants and the new species formed as result of the
reaction are called products.
Example:
2Na(s) + 2H
2O 2NaOH(aq) + H
2(g)
Reactants products

3. Identificatio? of Chemica? Reactio?
A chemical reaction can be identified by either of the following observations:
★Change in state
★Change in colour
★Evolution of gas
★Change in temperature
★Formation of precipitate

4. Chemica? equation
A chemical equation is the symbolic representation of a chemical reaction.
A chemical equation can be written in 3 forms:
★Word equation(ex: Hydrogen + Oxygen Water )
★Paragraph (ex: when hydrogen is combined with oxygen, water is formed)
★Symbolic representation (ex: 2H2 + O2 2H2O )

5. Balance? chemica? equatio?
A balanced chemical equation is that in which the total number of atoms of each element are
equal on both sides of the equation.

6. Makin? ? chemica? equatio? mor? informativ?
The physical states of the reactants and products can be represented by using the symbols, (s)
for solid, (l) for liquid, (g) for gas and (aq) for aqueous solutions.
The word (aq) aqueous is written if the reactant or product is present as a solution in water
Example:
2Na(s) + 2H
2O(l) 2NaOH(aq) + H
2(g)
Precipitate can also be represented by using an arrow pointing downwards ( ) instead of
using symbol (s).
Gaseous state of an evolved gas can be represented by using an arrow pointing upward
direction ( ) instead of using symbol (g).

7. Type of chemica? reaction
Combination
reaction
Decomposition
reaction
Exothermic
and
endothermic
reactions
Displacement
reaction
Oxidation
and reduction

8. Combinatio? reactio?
A reaction in which two or more reactants combine to form a single product, is called
combination reaction.
Example:
Calcium oxide reacts vigorously with water to form calcium hydroxide. The reaction is
highly exothermic, as a lot of heat is produced during the reaction.
CaO(s) + H
2O Ca(OH)
2(aq) + Heat
General equation:
A + B -------> AB

9. Decompsitio? reactio?
A reaction in which a single reactant breaks down to form two or more products, is
known as decomposition reaction.
1)Thermal decomposition
Those reactions use the energy in the form of heat for decomposition of the
reactant.
Ex: CaCO
3
(s) CaO(s) + CO
2
(g)
Heat
General equation:
AB -------> A + B

10. 2) Electrolysis
These reactions involve the use of electrical energy for the decomposition of the
reactant molecules.
Example: 2 H
2O 2 H
2 + O
2
3) Photolysis
These reactions involve the use of light energy for the purpose of decomposition.
Example : 2NaCl 2Na + Cl
2
Electric current

11. Exothermi? an? endothermi? reaction
The reactions which are accompanied by the evolution of heat are called exothermic
reactions or the reactions in which heat is released along with the formation of products
are called exothermic reactions.
Example : CH
4 + 2O
2 CO
2 + 2H
2O + Heat
The reactions which occur by the absorption of heat/energy are called endothermic
reactions.
Example: 6CO
2 + 12H
2,O C
6H
12O
6 +6 O
2 +6 H
2O

12. Displacemen reactio?
When a more reactive element displaces less reactive element from its compound, it is called
displacement reaction.
(i) Single displacement reaction : It is a type of reaction where an element reacts with a compound
and takes the place of another element in that compound is called single displacement reaction.
Example: Zn + CuSO
4 ZnSO
4 + Cu
(ii) Double displacement reaction: the reaction in which two different ions or group of atoms in
different ions or group of atoms in the reactant molecules are displaced by each other is called
double displacement reaction. Also called as precipitate reaction.
Example: Na
2SO
4 + BaCl
2 BaSO
4 + 2 NaCl

13. Neutralization reaction
The reaction in which acid react with base to form salt and water
are called neutralisation reaction
Example: NaOH + H
2SO
4 Na
2SO
4 + H
2O

14. Oxidatio? an? reductio? reaction
Oxidation Reduction
★Addition of oxygen
2Cu + O
2 → 2CuO
★Reduction of oxygen
2KClO
3 → 2KCl +3O
2
★Removal of hydrogen
2H
2S + O
2 → 2S + 2H
2O
★Addition of hydrogen
2Na + H
2 → 2NaH
★Removal of electrons (e
-
)
Zn

→ Zn
2+
+ 2e
-
★Addition of electrons (e
-
)
Zn
2+
+ 2e
-
→ Zn

15. Oxidising agent The substance which can bring about oxidation of other
substances is called an oxidising agent.
Reduction agent The substance which can bring about reduction of other
substances is called a reducing agent
Redox reactions Those reactions in which oxidation and reduction take place
simultaneously are called redox reactions.
Example: CuO + H
2 → Cu + H
2O

16. Corrosion
The phenomenon due to which open surface of the metals are slowly eaten away by
the reaction of air, water and chemicals present in the atmosphere, is called
corrosion.
The process of corrosion of iron is called rusting.
Painting, galvanising, electroplating are some of the methods to prevent corrosion.

17. Rancidity
It is the process of slow oxidation of oil and fat present in the food materials resulting
in the change of smell and taste.
Methods to prevent rancidity:
★Keeping food in airtight containers
★Refrigerating food at low temperatures
★Packing food in packets containing nitrogen
★Avoid keeping cooked in direct sunlight
★By adding antioxidants (Butylated Hydroxy Anisole; Butylated Hydroxytoluene)

18. I hope you all understood