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The process by which a chemical change takes place is called as chemical reaction. Those substances that take part in a chemical reaction are called reactants. Those substances which are formed after a chemical reaction are called products.

Word equation

The chemical reaction which is expressed in terms of full names of reactant and product molecules is called word equation. For example, Hydrogen reacts with oxygen to produce water.

Chemical Reaction Hydrogen + oxygen→Water
Chemical Reaction Hydrogen + oxygen→Water

Hydrogen + oxygenWater

(Reactants) (Products)

Chemical equations

The chemical reaction which is expressed by using molecular formulae of reactants and products is called chemical equation. The chemical equation is also called formula equation.

2 H2 + O2→2 H2O

Skeletal chemical equation

The chemical equation in which the total number of atoms of each element in reactant and product is not equal is called an unbalanced chemical equation or skeletal chemical equation. Some examples:

  • Sodium + Chlorine→Sodium chloride
  • Nitrogen + Hydrogen→Ammonia
  • Zinc + Hydrochloric acid →Zinc chloride + Hydrogen

Drawbacks of skeletal chemical equation

  • Skeletal chemical equation does not follow the law of conservation of mass.
  • It does not tell about the ratio of reactant and product molecules.
  • It does not give information about the total number of atoms of each element in reactants and products.
  • It is essential to balance the chemical equation because a balanced chemical equation satisfies the law of conservation of mass in chemical reaction.


Avogadro's Number
The molecular weight of a substance expressed in grams is known as its gram molecular weight. For example, gram molecular weight of methane is 16 because its molecular weight is 16. A gram molecular weight is equal to the weight of 6.023 × 1023 molecules. This number (6.023 × 1023) is called Avogadro's number or one mole.
For example:
16 grams of oxygen atom (1 mole)
= 6.023 × 1023 Oxygen atoms
32 grams of Oxygen molecule (1 mole)
= 6.023 × 1023 Oxygen molecule.

  • The process by which a chemical change takes place is called as chemical reaction.
  • The chemical reaction which is expressed in terms of full names of reactant and product molecules is called word equation.
  • The chemical reaction which is expressed by using molecular formulae of reactants and products is called chemical equation.
  • The chemical equation in which the total number of atoms of each element in reactant and product is not equal is called an unbalanced chemical equation or skeletal chemical equation.
.

Very Short Questions

Matter is anything that occupies space and has weight. Matter exists in three states, they are: solid, liquid and gas. For example: ice (solid), water (liquid) and steam (gas).

The process in which new substances with different properties are formed is called chemical reaction. In a chemical reaction, the exchange, combination or decomposition of molecules in a matter takes place.
For example:
Zinc + Hydrochloride acid → Zinc chloride + Hydrogen is a chemical reaction between Zinc and Hydrochloride acid.

The chemical equation is the method of representing a chemical reaction with the help of symbols and formulae of the substances involved in it.

The substances which combine or react are called reactants.

The new substances produced in a chemical reaction are called products.

The chemical equation represented by word is called word equation. Examples are:

  • Water Electrolysis→ Hydrogen + Oxygen
  • Potassium chloride Heat→ Potassium chloride + Oxygen.

The chemical equation represented by a chemical formula is called formula equation. For example:

  • 2H2O Electrolysis→ 2H2 + O2
  • 2KClO3 Heat→ 2KCl + 3O2

Five limitations of a chemical equation are as follows:

  • The physical state of reactants and products.
  • Rate of chemical equations.
  • Concentration of reactants and products.
  • Duration of chemical reaction.
  • The conditions of necessary for chemical reaction.

A catalyst is a chemical substance which increases or decreases the rate of chemical reaction without itself being charged at the end of chemical reaction.

The catalyst which increases the rate of reaction iis called positive catalyst. For example:
2KClO3 →240°C 2KCl + 3O2


2H2O2 MnO2→ 2H2O + O2
In above chemical reactions, MnO2 acts as a positive catalyst.

The catalyst which decreases the rate of chemical reaction is called negative catalyst. For example: 2H2O2 →Glycerine 2H2O + O2
Here, glycerine is a negative catalyst.

There are 4 types of chemical reactions on the basis of their nature. They are:

  • Addition or combination reaction
  • Decomposition or dissociation reaction
  • Displacement reaction
  • Acid-Base or neutralization reaction

The chemical reaction in which two or more reactants combine together to give a single product is called addition reaction. For example:
N2 + 3 H2 → 2NH3
C + O2 → CO2
C + 2H2 → CH4
Fe + S → FeS
C + 2S → CS2

The chemical reaction in which a single reactant is broken down into two or more than two products is called decomposition reaction. For example:
CaCO3 →Δ CaO + CO2
2KClO3 →Δ 2KCl + 3O2
CuCO3 →Δ CuO + CO2

The chemical reaction in which an element (or radical) in a compound is displaced by another element (or radical) to form a new compound is called displacement reaction. For example:

Single displacement reaction:
Zn + H2SO4 → ZnSO4 + H2
Mg + ZnCl2 → MgCl2 + Zn

Double displacement reaction:
AgNO3 + NaCl → NaNO3 + AgCl
HgCl2 + 2Kl → 2KCl + Hgl2

The chemical reaction in which an acid reacts with a base to form a salt and water is called acid-base reaction. For example:
HCl + NaOH → NaCl + H2O
H2SO4 + CaO → CaSO4 + H2O

Molecular weight is the sum of the atomic weight of all of same or different elements present in a molecular. For example:

Molecular weight of CH4 = C + H x 4
= 12 + 1 x 4
= 16

Molecular weight of O2 = O x 2
= 16 x 2
= 32

The molecular weight of a substance expressed in grams is known as its gram molecular weight. For example, gram molecular weight of methane is 16 because its molecular weight is 16.

A gram molecular weight is equal to the weight of 6.023 × 1023 molecules. This number (6.023 × 1023) is called Avogadro's number or one mole.
For example:
16 grams of oxygen atom (1 mole)
= 6.023 × 1023 Oxygen atoms
32 grams of Oxygen molecule (1 mole)
= 6.023 × 1023 Oxygen molecule.

Solution,
Here,
Molecular weight of H2O = 1 × 2 + 16 = 18
18 gram of water molecule = 6.023 × 1023 molecules of water.
i.e. 6.023 × 1023 molecules of water = 18 gm of water molecule.
∴ 1 molecule of water = 18 / (6.023 × 1023)
= 2.99 × 10-23 gm of water molecule.

When a burning piece of magnesium is inserted into an oxygen jar, then magnesium oxygen is formed.
2Mg + O2 → 2MgO

When limestone is heated, it decomposes into lime and carbon dioxide.
CaCO3 →Δ CaO + CO2

When hydrogen peroxide is electrolyzed in present of MnO2, then it decomposes into water and oxygen.

2H2O → MnO2 Electrolysis 2H2O + O2

When acid water is electrolyzed, air decomposes into Hydrogen and Oxygen.

2H2O →Electrolysis 2H2 + O2

Magnesium chloride and Hydrogen are produced.
Mg + 2HCl → MgCl + H2

Calcium chloride, water and carbon dioxide is produced.
CaCO3 + 2HCl → CaCl2 + H2O + CO2

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  • What is involved in a chemical reaction?

    Composition
    Delocalization
    Transformation
    Addition
  • Convert this word equation into chemical equation: Sodium Bicarbonate and Nitric acid gives Sodium nitrate and Carbon dioxide and water

    NaHCO3 + HNO3 ----> Na2NO3 + CO2 + H2O
    NaHCO3 + HNO2 ----> NaNO2 + CO2 + H2O
    NaHCO3 + HNO3 ----> NaNO3 + CO2 + H2O
    Na(HCO3)2 + HNO3 ----> Na(NO3)2+ CO2 + H2O
  • When is a false regarding chemical reaction?

    Reactants are the starting material needed to initiate chemical reaction
    Balancing a reaction means balancing the mass of each atoms on reactant and product side
    Irreversible reaction is denoted by a double arrow
    Endothermic reaction requires heat and exothermic reaction produces heat
  • What is not written above or below the arrow when writing a chemical equation?

    catalyst
    heat
    reagents
    Product
  • Which is false about chemical equation?

    A chemical equation tells us about the rate of the reaction
    It gives idea about ratio of reactant and product molecules
    It represents the type of Chemical reaction
    It gives idea about ratio of molecular weight of reactant and product
  • In chemical equation a double headed arrow symbolizes

    Multi-directional reaction
    Irreversible reaction
    Reversible reaction
    Dynamic reaction
  • Which is the most dangerous gas in the world?

    Potassium cynide(KCN)


    NaCN


    NaOH


    HCL


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