Give my overview of
Chapter - Chemical
Reactions and equation
Answers
Answer:
Chemical Reactions and Equations
Any process that involves the rearrangement of structure of the substance or conversion of reactants into products is defined as Chemical Reaction.
For a Chemical Reaction to occur, the change can be observed in the form of -
Change in State: Melting of ice into water.
Change in Colour: Iron rusting which has colour change from silver to reddish brown.

Change in Temperature: There are two types of reaction i.e Exothermic and Endothermic Reaction.
Exothermic Reactions: Those reactions in which energy is released in the form of heat are called Exothermic Reactions.
Examples -
(1) All combustion reactions e.g.
CH4+ 2O2 —> CO2 + 2H2O + Heat
(2) Thermite reactions e.g.
2A1 + Fe2O3 —> 2Fe + Al2O3 + Heat
Combinations are generally exothermic in nature. The decomposition of organic matters into compost is an example of exothermic reaction.
Endothermic Reactions: Those reactions in which energy is absorbed are called Endothermic Reactions.
Examples -

also, the reaction of photosynthesis -

Evolution of any gas: When Zinc reacts with sulphuric acid it gives hydrogen gas.
Zn + H2 SO4 → ZnSO4 + H2
Formation of Precipitate: When a soluble carbonate reacts with Barium, Barium Carbonate precipitate can be observed.
Change in State
Some chemical reactions are characterized by a change in state.
When wax is burned (in the form of wax candle,) then water and carbon dioxide are formed.
Now, wax is a liquid whereas carbon dioxide is a gas. This means that during the combustion reaction of wax, the physical state changes from solid to liquid and gas.
Physical Change
In this change identity of the substance remains same.
For Example, Melting, Boiling etc.
Chemical Change
The identity of the substances change
Reactants are converted into substance due to formation or broken down of older bonds

Chemical Equation
The symbolic representation of chemical reaction using symbols and formulae is known as Chemical Equation. For this, reactants are written in left hand side whereas products are written on the right.
Balanced Chemical Equation
A balanced chemical equation is the one where the number of atoms involved in reactants side is equal to number of atoms on product side.

Eq.1. Example of Balanced Chemical Equation
Steps to form Balanced Equation
To show how to balance the equation, the following equation is used-
Fe + H2O → Fe3O4 + H2
Step 1: First of all, draw the boxes around each formula as shown below-

Step 2: Find out the number of atoms of each element. For Example, on reactant side, 1 for Fe, 2 H, and 1 O and on product side we have, 3 for Fe, 4 for O and 2 for H.
Step 3: Start to balance the equation with the compound having maximum number of atoms. While balancing does not alter the formula of the compound.
Step 4: One by one balance each element on reactant and product side.

Step 5: After balancing number of atoms on both the side of the equation, finally check the correctness of the balanced equation.

Step 6: then write the symbols of the physical state of reactants and products as shown below-
3Fe(s) + 4H2O (g) → Fe3O4 (s) + 4H2 (g)
This above equation represents the balanced equation.
Balancing a Redox Reaction
The basic ionic form of the equation is-
Fe2+ + Cr2O72- → Fe3+ + Cr3+
Oxidation half reaction is-

Reduction half reaction is-

Use the reduction half method to balance the equation. Balance the atoms in each half of the reaction except H and O atoms.
Cr2O72- (aq) → 2 Cr3+(aq)
Add water molecules as the reaction is taking place in acidic solution. This is to balance the O atoms and hydrogen ions.
Cr2O72- (aq) + 14 H+(aq) → 2 Cr3+(aq) + 7H2O (I)
Then balance the charges in both half reactions.
Fe2+(aq) → Fe3+(aq) + e-
Cr2O72- (aq) + 14 H+ + 6e- → 2 Cr3+ + 7H2O
6 Fe2+(aq) → 6 Fe3+(aq) + 6e-
Two half of the equations are added to get the overall reaction
6Fe2+(aq) + Cr2O72-(aq) + 14H+(aq) → 6Fe3+(aq) + 2Cr3+(aq) + 7H2O (I)
Types of Chemical Reaction
Combination Reaction is reaction when single product is formed from the combination of two or more reactants. For Example-

Eq.2. Example of Combination Reaction
Reactions can be exothermic as well as endothermic. Exothermic reaction release heats and raises the temperature of the surroundings. For Example, Respiration is an example of exothermic reaction.

Eq.3. Example of Exothermic Reaction
Endothermic reaction involved the absorption of the heat and thus it cools the surrounding. The decomposition of dead organic material is an endothermic reaction.
Decomposition Reaction is type of reaction which involves breakdown of single reactant into simpler products. Decomposition of silver chloride into silver and chlorine in presence of sunlight is an example of decomposition reaction.

Eq.4. Example of Decomposition Reaction
Displacement Reaction is a reaction in which more reactive element will displaces the less reactive element.
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Chemical Reaction:-
A chemical reaction or a chemical change is a process in which one set of chemicals,called as reactants is transformed into another set called the products.
Characteristics of Chemical Reactions
A chemical reaction is a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products.
Example: Rusting of iron, the setting of milk into curd, etc.
Reactant: The chemical substance which takes part and undergoes a chemical change.
Product: The new substance which is formed after a chemical change.
Observations for a chemical change:
•Change in state of a substance.
•Change in colour of a substance.
•Change in temperature
•Evolution of heat
•Absorption of heat.
•Evolution of gas.
•Evolution of light and sound
Chemical equation:
The representation of the chemical reaction using symbols of substances.
Example: A + B ⇨ C + D
Balanced Chemical Equation:
A chemical equation having an equal number of atoms on both sides of the reaction is called a balanced chemical reaction.
E.g., Zn + H2 SO4 ⇨ ZnSO4 + H2
Balancing equations:
•The same number of atoms of reacting elements on both sides of the equation.
•An element which appears in only one reactant and one product should be balanced first.
•Alternately, choose the compound with a maximum number of participating atoms.
•Never change the formulae of compounds, only coefficients should be added.
•Law of Conservation of Mass applies to all chemical reactions.
Types of Chemical Reactions
Combination Reaction or synthetic reaction:
A combination reaction is a reaction where two or more reactants combine under suitable conditions to form a new substance. As a new substance is being formed, this type of reaction is also called as a synthesis reaction.
A + B ⇨ AB
Decomposition Reaction:
Reactions in which one compound decomposes in two or more compounds or elements are known as Decomposition Reactions. A decomposition reaction is just opposite of combination reaction.
AB ⇨ A + B
3 types of decomposition reaction:-
•Thermal decomposition is a chemical reaction where a single substance breaks into two or more simple substances when heated.
•Electrolytic decomposition may result when an electric current is passed through an aqueous solution of a compound. (eg. water)
•Photochemical decomposition is a chemical reaction in which a substance is broken down into simple substances by exposure to light.
Displacement reaction:
Reactions in which atoms or ions move from one compound to other to form a new compound are known as Displacement reaction.
•Single-Displacement reaction:
(X+YZ⟶XZ+Y) e.g. Fe+CuSO4⟶FeSO4+Cu
•Double-displacement reaction (XY+WZ⟶WZ+WY)
Few common Double-displacement reactions are:
Precipitate formation: Pb(NO3)2+2KI⟶2KNO3+PbI2 (yellow lead iodide precipitate)
Water formation (Acid-base reaction): HCI+NaOH⟶NaCI
Exothermic and Endothermic reaction:
A reaction can either be endothermic or exothermic. An exothermic reaction is a chemical reaction that gives out energy (mostly in the form of heat and light) and an endothermic reaction is a reaction which takes in energy from the surroundings.
Oxidation reaction :-
addition of oxygen and removal of hydrogen
Reduction reaction:-
addition of hydrogen and removal of oxygen
Redox reaction :- oxidation+ reduction
Neutralization reaction :- acid + base ---> salt + water
Effects of Oxidation Reactions in Our Daily Life:
Corrosion: It is an undesirable change that occurs in metals when they are attacked by moisture, air, acids and bases.
Example, Corrosion (rusting) of Iron: Fe2O3. nH2O (Hydrated iron oxide)
Rancidity: Undesirable change that takes place in oil containing food items due to the oxidation of fatty acids.
Preventive methods of rancidity: Adding antioxidants to the food materials, storing food in the airtight container, flushing out air with nitrogen gas and refrigeration.