Chemical Reactions And Equations Class 10 notes

chemical changes:when a substance combines with another to form one or more new substance with different physical and chemical properties called chemical changes

for exmple

magnesium ribbon burns with adazzling white flame and changes into a white powder. This powder is magnesium oxide.
Mg + O₂ → MgO

Physical change – Physical changes can include changing the color, shape, state of matter, or volume of a substance but no new substance is formed.
Example: Boiling water evaporating.
Hot shower water turning to steam.

Chemical reaction:
Chemical reaction are the process in which new substance formed with new properties

observations helps us to determine whether a chemical reaction has taken place –
change in state
change in colour
evolution of a gas
change in temperature.

CHEMICAL EQUATIONS
A method of expressing chemical reaction in words or sentence rather than chemical formulas. it helps identify the reactants and products in a chemical reaction. for example
The word-equation for the above reaction would be
Magnesium + Oxygen → Magnesium oxide

Writing chemical equations
A method of representation of a chemical reaction in with the help of symbols and chemical formulae of the reactants and products is known as a chemical equation.

Balancing of a Chemical Reaction

Balanced chemical equation
The chemical equation in which the number of atoms of each element in the reactants is equal to that of the products is called a balanced chemical equation. or we can say a balance chemical reaction have equal number of atom of differen element on reactants and product side

why we balance the chemical equation

Ans::As we know chemical reactions follow the law of conservation of mass. In law of conservation of mass ,"matter can neither be created nor destroyed in a chemical reaction" it mean total mass of all the reactants must be equal to the total mass of the product .So we have to make the number of different type of atom equal on both side of a chemical equation is konwn as balance the chemical equation. So the chemical equation are balance to satisfy the law of conservation of mass.

Balancing of chemical equation
The equation are balance by hit and trial method. Let take an example to understand the balancing chemical equation
Zinc + Sulphuric acid ® Zinc sulphate + Hydrogen

Zn + H₂SO₄ → ZnSO₄ + H₂

here number of atoms of different elements on bothsides of the reactants and products .

Element	Number of atoms in reactants (LHS)	Number of atoms in products (RHS)
Zn	1	1
H	2	2
S	1	1
O	4	4

As the number of atoms of each element is the same on both sides reactants and products then it is a balanced chemical equation.

Let us try to balance the following chemical equation – Fe + H₂O → Fe₃O₄ + H₂
Step I: let count the number of atoms of different elements present in the unbalanced equation

Element	Number of atoms in reactants (LHS)	Number of atoms in products (RHS)
Fe	1	3
H	2	2
O	1	4

Step II: select the element which has the maximum number of atoms. Using these criteria, we select Fe₃O₄ and the element oxygen in it. There are four oxygen atoms on the RHS and only one onthe LHS.

Atom of Oxygen	atoms in reactants	atoms in products
intinal	1 in (H2O	4 in (Fe3O4)
To Balance	1 x 4	4

Now the partly balanced equation becomes –
Fe + 4H₂O → Fe₃O₄ + H₂ Step III: Fe and H atoms are still not balanced. Pick any of these elements to proceed further. Let us balance hydrogen atoms in the partly balanced equation.

Atom of Hydrogen	atoms in reactants	atoms in products
intinal	8 in (H2O	2 in (H2)
To Balance	8	2 x4

Now the partly balanced equation becomes –
Fe + 4H₂O → Fe₃O₄ + 4H₂
Step IV: only one element is left to be balanced, that is, iron.

Atom of Iron	atoms in reactants	atoms in products
intinal	1 ( in Fe)	3 (in Fe3O4)
To Balance	1	1 x3

Now the partly balanced equation becomes –
3Fe + 4H₂O → Fe₃O₄ + 4H₂
Step V: Finally, to check the correctness of the balanced equation, we count atoms of each element on both sides of the equation.
3Fe + 4H₂O → Fe₃O₄ + 4H₂

TYPES OF CHEMICAL REACTIONS
Some important type of chemical reaction are
Combination Reaction
Decomposition Reaction
Displacement Reaction
Double displacement Reaction
Oxidation and Reduction reaction

1:Combination Reaction

we can say that when two or more substances (elements or compounds) combine to form a single product, the reactions are called combination reactions. For Example

(i) Burning of coal
C(s) + O₂(g) → CO₂(g)
(ii) Formation of water from H2(g) and O2(g)
2H₂(g) + O₂(g) → 2H₂O(l)
(iii) Formation of water from chlorine and Hydrogen
H₂(g) + Cl₂(g) → 2HCl(g)
(ii) Formation of water from Sodium and chlorine
2Na₂(s) + Cl₂(g) → 2NaCl(s)

2 :Decomposition Reaction
A reaction in which single reactant breaks down into one or more simpler Substance products are know as Decomposition Reaction for example


Note: Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating is an important decomposition reaction used in various industries. Calcium oxide is called lime or quick lime. It has many uses – one is in the manufacture of cement. When a decomposition reaction is carried out by heating, it is called thermal decomposition.
CaCO3(s) → CaO(s) + CO2(g)

3 :Displacement Reaction
Those reaction in which higer reactive element take place of less reactive element in compound is called Displacement Reaction for example

Zinc and lead are more reactive elements than copper. They displace copper from its compounds.

4 :Double Displacement Reaction
those reaction in which two compound react by an exchange of ions to form two new compounds are called Double Displacement Reaction for example

:Oxidation and Reduction
1:Oxidation
The addition of Oxygen and removal of hydrogen in reaction are known as Oxidation

2 : Reduction
The addition of Hydrogen and removal of Oxygen in reaction are known as Reduction

Redox reaction
one reactant gets oxidised while the other gets reduced during a reaction. Such reactions are called oxidation-reduction reactions or redox reactions.

ZnO + C → Zn +CO
MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂

Exothermic reaction
A Reactions in which energy is release are known as exothermic reactions.
CH₄ + O₂ → CO₂ + H₂O + Heat

Endothermic reactions
Reactions in which energy is absorbed are known as endothermic reactions.
NH₄Cl (s) + H₂O (l) ⟶ NH₄Cl (aq) – Heat

corrosion
When a metal is attacked by substancesaround it such as moisture, acids, etc., it is said to corrode and this process is called corrosion.
4Fe(s) + 3O₂ + xH₂O → 2Fe₂O₃.x H₂O
Corrosion of copper:
Cu(s) + H₂O(moisture) + CO₂(from air) → CuCO₃.Cu(OH)₂(green)

Rancidity
the oxidation of fats and oils in food that is kept for a long time. It gives foul smell and bad taste to food. Rancid food causes stomach infection on consumption. Prevention
(i) Use of air-tight containers
(ii) Packaging with nitrogen
(iii) Refrigeration
(iv) Addition of antioxidants or preservatives