सरस्वती वंदना (रविरुद्र पितामह विष्णुनुतं )

 

रविरुद्र पितामह विष्णुनुतं ।

हरिचंदन कुंकुंम पंकयुतं ।।

मुनिवृन्द गणेन्द्र समानयुतं ।

तव नौमी सरस्वती पादयुगं ।।

शशि शुद्ध सुधा हिम धाम युतं ।

शरदम्बर बिम्ब समान करं ।।

बहुरत्न मनोहर कान्तियुतं ।

तव नौमी सरस्वती पादयुगं ।।

कनकाब्ज विभूषित भूति भवं ।

भव भाव विभाषित भिन्न पदं ।।

प्रभुचित समाहित साधु पदं ।

तव नौमी सरस्वती पादयुगं ।।

भवसागर मज्जन भीतिनुतं ।

प्रतिपादित संततिकारमिदं ।।

विमलादिक शुद्ध विशुद्ध पदं ।

तव नौमी सरस्वती पादयुगं ।।

मतिहीन जनाश्रय पादमिदं ।

सकलागमभाषित भिन्न पदं ।।

परिपूरित विश्वमनेकभवं ।

तव नौमी सरस्वती पादयुगं ।।

परिपूर्णमनोरथ धामनिधिम ।

परमार्थ विचार विवेक निधिम ।।

सुरयोषित सेवित पादतलं ।

तव नौमी सरस्वती पादयुगं ।।

सुरमौली मणिद्युति शुभ्रकर ।

विषयादि महाभय वर्णहरं ।।

निजकान्ति विलेपित चंद्र शिवं।

तव नौमी सरस्वती पादयुगं ।।

गुणनैक कुलस्थिति भीतिपदं ।

गुण गौरव गर्वित सत्यपदं ।।

कमलोदर कोमल पादतलं ।

तव नौमी सरस्वती पादयुगं ।।

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Chemical Reactions and Equations (Class 10 Science) Part 3

 

Types of chemical reaction

The chemical reaction are classified into different classes depending upon the type of chemocal changes taking place. These reactions are as follows :

 

1.  Combination Reaction :-

          A reaction in which two or more reactants combine to form a single product, is called combination reaction, e.g.

 

CaO_(s) + H₂O_(l) → Ca(OH)_2(aq) + Heat

 

C_(s) + O_2(g)   →   CO_2(g)

 

2.  Decomposition Reaction :-

          A reaction in which a single reactants breaks down to form two or more products, is known as decomposition reaction. This reaction is opposite to combination reaction. e.g.

CaCO_3(s)  →  CaO_(s)  +  CO_2(g)

 

2AgCl_(s)  →  2Ag_(s) +  Cl_2(g)

 

2NaCl_(l)  →  2Na_(s)  +  Cl_2(g)

 

 

3.  Exothermic and Endothermic reaction :-

          Depending upon whether heat is evolved or absorbed during a reaction, the reaction can be exothermic or endothermic.

(i)Exothermic reactions :-  The reaction which are accompanied by the evolution of heat, are called exothermic reactions or the reaction in which heat is released along with the formation of products are called exothermic reaction. e.g.

a)    Burning of natural gas

CH_4(g)  +  2O_2(g)  →  CO_2(g)

b)   Burning of Magnesium ribbon

2Mg_(s) + O_2(g)  →  2MgO_(s)  +  Heat

(ii)     Endothermic reaction :-  The reaction which occur by the absorption of heat/energy are called endothermic reactions. e.g.

6CO_2(aq)  +  12H₂O_(l)  →  C₆H₁₂O₆ + 6O₂ + 6H₂O

NH₄Cl_(s) + Heat → NH_3(g)  +  HCl_(g)

 

4.  Displacement reaction :-

          When a more reactive element displaces less reactive elwmwnt from its compound, it is called displacement reaction. this reaction is of two types :

(i)    Single displacement reaction :  It is a type of chemical reaction where an element reacts with a compound and takes the place of another element in that compound is called single displacement.

        Zn_(s)   +  CuSO_4(aq)  →  ZnSO_4(aq)  +  Cu_(s)

(ii)    Double displacement reaction :  The reaction in which two different ions or group of atoms in the reactant molecule are displaced by each other is called double displacement reaction.

Na₂SO_4(aq) + BaCl_2(aq)  →  BaSO_4(s)  +  2NaCl_(aq)

 

5.  Oxidation and Reduction reaction :-

OXIDATION :

          It can be defined as

The process in which oxygen is added to a substance.

Or

The process in which hydrogen is removed from a substance.

Or

The process in which a substance loss electrons.

e.g.

2H₂S  +  O₂  →  2S  +  2H₂O

2Cu  +  O₂  →  2CuO

 

REDUCTION :

          It can be defined as

The process in which oxygen is removed from a substance.

Or

The process in which hydrogen is added to a substance.

Or

The process in which a substance gains electrons.

e.g.

2Na  +  H₂  →  2NaH

Zn₂+  +  2^e−  →  Zn

 

Oxidising agents :  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 substance is called a reducing agent.

 

Redox Reaction :-

          Those reaction in which oxidation and reduction take place simultaneously, are called redox reactions. e.g.

CuO  +  H₂  →  Cu  +  H₂O

          In this reaction the copper oxide is losing oxygen and is being reduced. Whereas oxygen is added to hydrogen and is being oxidised.

 

 

 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.

e.g. Iron articles are shiny when new, but get coated with a reddish brown powder when left for some time.

The process of corrosion of iron is Calles rusting. The rusting of iron is a redox reaction. the black coating on silver and the green coating on copper are other examples of corrosion.

Painting, Galvanising, electroplating are some of the methods to prevent corrosion.

 

Effects of Corrosion

(i)              Corrosion causes damages to car bodies, bridges, iron railings, ships, and all objects made up of metals, specially those which are made up of iron.

(ii)           Corrosion is a wasteful process in most of cases. Every year tons of various metals especially iron get wasted in the country.

 

Rancidity

 

It is the process of slow oxidation of oil and fat present in the food material resulting in the change of smell and taste in them. The method to prevent rancidity are :

(i)              Keeping food material in air tight containers.

(ii)           Refrigeration of cooked food at low temperature.

(iii)        Packing of food items like potato wafers etc in packets containing nitrogen gas instead of air.

(iv)         Avoid keeping cooked food and food materials in  direct sunlight.

 

Part 1        Part 2

 

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Chemical Reactions and Equations (Class 10 Science) Part 2

 

Balanced chemical equation

            A balanced chemical equation is that in which the total number of atoms of each element are equal on both sides of the equation. The balancing of a chemical equation is based on law of conservation of mass. According to this – “mass can neither be created nor be destroyed during a chemical reaction.”

 

            The method used for balancing chemical reaction is called hit and trial method as we make trials to balance the equation by using the smallest whole number coefficient. In this method the number of atoms of each element remains the same, before and after a chemical reaction.

 

BALANCING A CHEMICAL EQUATION

            Several steps are involved in balancing a chemical equation. These steps are as follows :-

Step (a) Writing unbalanced equation and enclosing the formulae in brackets.

(Na) + (H₂O) → (NaOH) + (H₂)

 

Step (b) Making list of number of atoms of different atoms of different elements as present in unbalanced equation.

Element	Number of Atoms in Reactants (LHS)	Number of Atoms in Products (RHS)
Na	1	1
H	2	3
O	1	1

 

Step (c) Balancing first element

            From the table shown above, it is clear that it is only the hydrogen atoms, which are unbalanced. So , firstly we try to balance it.

Atoms of H	In reactants	In products
Initialy	2 (in H2O)	3 (1 in NaOH and 2 in H2)
To Balance	2x2	2x1 in NaOH 2 in H2 = 4H atoms

Step (d) Balancing second element

            We examine the obtained equation and select another element which is still unbalanced. In the above equation, Na is still unbalanced. To balance the number of Na- atoms,

Atoms of Na	In reactants	In products
Initialy	1 in (Na)	2 (in NaOH)
To Balance	2x1	2

 

Thus after balancing Na and removing the brackets, we get the equation:

2Na + 2H₂O → 2NaOH + H₂

 

Step (e) Balancing other element

            If we further examine the reaction, no element is found to be unbalanced. This method of balancing chemical equation is called hit and trial method.

 

Step (f) Checking the correction of equation

            To check the correctness of the equation, we further tabulate the number of atoms of each element separately.

 

Element	Number of Atoms in Reactants (LHS)	Number of Atoms in Products (RHS)
Na	2	2
H	4	4
O	2	2

 

 Making a chemical equation more informative

(i)                The physical states of the reactants and products can be represented by using symbols, (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous solution.

(ii)             The specific conditions of the reaction like temperature, pressure, catalyst etc., are written above or below the arrow in the chemical equation.

(iii)           Evolution of heat or absorption of heat can be indicated by writing [+Heat] on the right hand side or left hand side of the equation.

Example –

C_(s) + O_2(g) → CO_2(g) + Heat

Mg_(s) + H₂SO_4(aq) → MgSO_4(aq) + H₂↑

part 1       Part 3

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Chemical Reactions and Equations (Class 10 Science) Part 1

Chemical Reactions

A chemical reaction is a change in which one or more substances or reactants reacts to to form new substances with different properties.

The reacting species (molecule, atom or ion) are known as reactants (the substances that undergo chemical change in the chemical reaction) and the new species formed as a result of the reaction are called products (the new substances formed during reaction).

 2Na_(s) + 2H₂O_(l) → 2NaOH_(aq) + H_2(g) ↑

In the above chemical reaction , sodium hydroxide and hydrogen are the products and sodium and water are the reactants.

 

 

Identification of chemical reaction

A chemical reaction can be identified by either of the following observations –

(i)                Change in state

(ii)             Change in colour

(iii)           Evolution of gas

(iv)           Change in temperature

(v)              Formation of precipitate

 

Chemical Equations

 

A chemical equation is the symbolic representation of a chemical reaction.

Methane  + Oxygen → Carbon dioxide + Water

This equation is called “ word equation”. The word equation can be changed in to a chemical equation by writting symbol and formulae of the substances in place of their name.

CH_4(g) + 2O_2(g) → CO_2(g) + 2H₂O(l)

 

Writing a Chemical Equation

A chemical equation shows a change of reactants to products through an arrow (→) placed between them.

On the left hand side (LHS) of the arrow reactants are written with a plus sign (+) between them. Similarly on the right hand side (RHS) , products are written  with a plus sign (+) between them.

            The arrow head points towards the products and shows the direction of the reaction.

Mg + O₂ → MgO

In the above equation, number of magnesium and oxygen atoms are not same on both sides of ab equation. Such an unbalanced equation is called skeletal chemical equation.

Part 2       Part 3

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