1. Chemical Reaction (Part 01)

1. Chemical Reaction 

(Part 01)

Q. How can you say that a change took place?

Or

How do we come to know that a chemical reaction has taken place?

Ans. By examining of the state, colour, temperature of the matter is change and excretion of gases etc we can say that the change took place.

Q. What do you mean by change? What are main types of changes?

Ans. Change: Which process alters the specific properties of a mater is called change.

There are two types of change:

01.  Chemical Change

02.  Physical Change

Q. What do you mean by Chemical change?

Ans. Chemical Change: In which reaction a new substance is formed is known as chemical change. This change altars the [1]chemical property of a substance.

OR

Any change in the chemical composition and its constituent or molecules of the substances is called chemical change.

2H₂ + O₂  → 2H₂O

In the chemical change or reaction reactants converted into the products. We cannot get the reactant from product. Like burning of candle, turning the milk into the curd.

Q. What are Reactant and Product in a chemical reaction?

Ans.  Look at the following equation where A and B are Reactants and C and D are Products.

Reactant: The substances took place in a reaction is known as reactant. In the given equation (2H₂ + O₂ → H₂O) H₂ and O₂ are the reactant.

Product: - The substances formed into the chemical reaction is known as product. In equation (2H₂ + O₂  → 2H₂O) H₂O is the product.  

Q. How can you say that a chemical reaction took place?

Or

How do we come to know that a chemical reaction has taken place?

Ans. If the colour, state and temperature of substance (or product) change, or any types of gas, smoke, vapour or bubbles are evaluate or any type of precipitate is form then we can say the chemical reaction took place.

Q. What are the main types of the chemical reaction on the bases of the state of reactant and products?

Or

What do you mean by the Autonomous and Heteronymous systems of the equations?

Ans.  Autonomous System: - The system in which the forms of the stages of the reactant and products are same is called Autonomous System.

2NO(g ) + O₂ (g)  →  2NO₂ (g)

Heteronymous System: - The system in which the form of the reactant and products are not same is called Heteronymous System.

2Mg(s) +O₂ (g) → 2MgO(s)

Q. What do you mean by the Physical Changes?

Ans. Physical Change: In which reaction a new substance is not formed but only physical properties alters is known as physical change. This change altars the physical property of a substance.

OR

Without Any change in the chemical composition and it constituent or molecules of the substances is called physical change.

In the physical change or reaction only physical properties changed so we can get the reactant from product. Like we can get the ice from the water and can convert this reaction also for getting water from the ice.

N2O2	Nitrous Oxide	Laughing Gas
NH3	Ammonia	Tear Gas

9. What do you mean by exothermic and endothermic reactions? Give examples.

Ans. Exothermic Reaction: - A reaction in which heat is evolutes is known as [2]exothermic reaction. It is also called the Thermit Reaction.

CH₄(g)+ 2O₂ (g) → CO₂(g)+2H₂O(l)+ Energy (890.4KJmol^-1)

Some other examples of exothermic reaction are:

2Al(s) + Fe₂O₃(s) → Al₂O₃(g) + 2Fe(l)

The energy produced in this reaction is used in wielding, to filling the Joints or cracks or railway tracks.

Endothermic Reaction: - A reaction in which heat is absorbed is known as endothermic reaction.

Ba(OH)₂.8H₂O (s)  +  2NH₄SCN (s)→ Ba(SCN)₂ (aq) + 2NH₃ (aq) + 10H₂O(l)

In this reaction the mixture is cooled down the very lower point and the conduction presented into the air freezes like ice particles.

1. Why should a magnesium ribbon be cleaned before burning in air? Ans. In moist air a layer of oxide is formed on the magnesium. To remove it we rubbed with sand paper before burning. This layer of oxide checks the further corrosion. 2. Write the balanced equation for the following chemical Reactions. (i) Hydrogen + Chlorine → Hydrogen chloride (ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride (iii) Sodium + Water → Sodium hydroxide + Hydrogen Ans. (i)       H2 + Cl2  → 2HCl (ii) BaCl2 + Al2(SO4) → BaSO4  + AlCl3            Balancing it  3BaCl2 + Al2(SO4)3→3BaSO4  +2AlCl3 (iii)     Na + H2O  →   NaOH  + H2 3. Write a balanced chemical equation with state symbols for the following reactions. (i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride. Ans. Barium chloride + Sodium sulphate → Barium sulphate + Sodium chloride.   BaCl2 + Na2SO4  →  BaSO4 + NaCl2 (ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water. Ans. Sodium hydroxide + Hydrochloric acid → Sodium chloride solution + Water.     NaOH + HCl  →  NaCl + H2O Q. The reaction which is used to filling the gapes or cracks of railway tracks is known as ---------------. Ans. Thermit Reaction

Q. What do your mean by Chemical Reaction? What are main types of Chemical Reaction?

Ans. The Chemical Reaction: In which reaction composition of a substance change is called Chemical reaction. A chemical reaction is a process of rearrangement of atoms.

Reactant   → Products

In the chemical reaction the reactant are written left of the arrow and the product after arrow.

There are many types of reaction:

01.  Combination Reaction.

02.  Decomposition Reaction.

a)      Thermal Decomposition Reaction

b)      Double Decomposition Reaction

c)      Electrolysis

03.  Displacement Reaction

04.  Double displacement Reaction.

05.  Precipitated Reaction

06.  Oxidation or reduction reaction

07.  Irreversible Reaction

08.  Reversible reaction

09.  Photochemical Reaction

01. Combination Reaction: - In which reaction two or more substance simply combines to form a new substance is called combination reaction.

CaO + H₂O →  Ca (OH)₂

Some other examples:

C + O₂  → CO₂        (Burning of coal)

2H₂ + O₂ → 2H₂O  (Formation of water)

02. Decomposition Reaction: In which reaction a chemical compound breaks down to produce two or more simple substance is called decomposition reaction.

2H₂O    → 2H₂   + O₂

2AgBr   → 2Ag  + Br₂

CaCO₃  → CaO + CO₂

[3]* (2AgCl  → 2Ag  + Cl₂ )

[4]* (2Fe SO₄→ Fe₂O₃  + SO₂ + SO₃)

2Pb(NO₃ ) → 2PbO  + 4NO₂ + O₂

There are three types of decomposition reaction:

a)      Thermal Decomposition Reaction

b)      Double Decomposition Reaction

c)      Electrolysis

a) Thermal Decomposition Reaction: When a substance decomposes on heating is called thermal decomposition. 

CaCO₃  → CaO + CO₂

2AgBr   → 2Ag  + Br₂

b) Double decomposition Reaction: - In which reaction the reactants decomposes into ions is displaces by each other. This type of displacement reaction is known as double decomposition reaction.

Na₂SO₄ + BaCl₂ →  NaCl₂  +   BaSO₄

Ba²⁺  +   SO₄ ^{2 –}   →      BaSO₄

c) Electrolysis: When decomposition reaction takes place by passing electric current is called electrolysis.

Electrolysis means Braking down with the help of electric. (Electro = Electric and lyses = breaks)

                 Electric

2H₂O → 2H₂ + O₂

03. Displacement Reaction: In which reaction a more active element is replaced or removed by another element to form a compound is called displacement reaction.

Zn + CuSO₄     → ZnSO₄ + Cu

Pb + CuSO₄    → PbSO₄ + Cu

Fe + CuSO₄     → FeSO₄ + Cu

Cu + AgNO₃    →  Cu (NO₃) ₂ + 2Ag

Note – in above reactions first three metals Zn, Pb an Fe are more reactive then Cu of CuSO₄. so that they displaced the Cu from their place. In fourth reaction Cu is more reactive then Ag.

04. Double Displacement Reaction: In which displacement reaction two different atoms or groups of atoms are displace by other atoms / group of atoms is called double displacement reaction.

KCl + AgNO₃   →   AgCl + KNO₃

Na₂SO₄ + BaCl₂  → NaCl₂ + BaSO₄

BaCl₂ + Na₂SO₄  → BaSO₄ + 2NaCl

1. A solution of a substance ‘X’ is used for white washing. (i) Name the substance ‘X’ and write its formula. (ii) Write the reaction of the substance ‘X’ named in (i) above with water. Ans.  (i) The Substance X is used to white washing is quick lime (Calcium Oxide) [CaO] (ii) CaO + H2O →  Ca (OH)2 2. Why is the amount of gas collected in one of the test tubes in Activity decomposition of water  double of the amount collected in the other? Name this gas. Ans. On electrolysis water decomposed Hydrogen and Oxygen according to the reaction in 2: 1. That is why Hydrogen emits double then oxygen.            2H2O → 2H2 + O2

05. Precipitated Reaction: - In which reaction the insoluble solid is formed this type of reaction is known as precipitated reaction. This insoluble solid is known as precipitate. Precipitate is denoted by down head arrow ( ↓) in the reaction.

Na₂SO₄ + BaCl₂ → NaCl2+ BaSO₄ ↓

In this reaction BaSO₄  is a precipitate. BaSO₄  is formed by Ba²⁺  and  SO₄ ^{2 –} 

Pb(NO₃)₂ + 2KI → _PbI2 ↓+ 2KNO₃ ↓

06. Redox Reaction: In which reaction One substance is oxidized and the other is reduced is called redox reaction. Oxidation and Reduction occur simultaneously.

CuO         → Cu + H₂O

                 Oxidation 

H₂ + O   ———>  H₂O

Fe₂O₃ + 2Al     ———>  Al₂O₃ + 2Fe

Zn + CuSO₄     ———> ZnSO₄ + Cu

Fe + S              ———> FeS

a) Oxidation Reaction: A reaction in which oxygen or an electro negative element is added is called an oxidation reaction.

Addition of oxygen or loosing of electron (Hydrogen) is called oxidation.

C + O₂             →         CO₂

2C + O₂           →          2CO

2H₂ + O₂         →         2H₂O

2Mg + O          →           2MgO

4Na + O           →           2Na₂O

S + O_{2                 →}           SO₂

Fe + S              →            FeS

b) Reduction Reaction: A reaction in which hydrogen or an electro positive element is added is called and Reduction reaction.

Addition of hydrogen or gaining of electron (or removing of Oxygen) is called Reduction.

2NH_{3                   →}            N₂ + 3H₂

MgO + C          →             Mg + CO

CuO + H_{2           →}             Cu + H₂O

ZnO + H_{2            →}             Zn + H₂O

Cl₂ + H₂           →              2HCl

CuO + H₂         →             Cu + H₂O

Oxidizing Agent: The substance, which oxidized the other substance in a chemical reaction, is known as oxidizing agene. Iodine acts as oxidizing agent.

Cu + I₂             → CuI₂

Reducing Agent: The substance, which reduced the other substance in a chemical reaction, is known as reducing agent. Copper acts as reducing agent.

Cu + I₂             → CuI₂

07. Irreversible Reaction: - In which reaction product cannot combined into reactants is called irreversible reaction. It is shown with sign of arrow.

C + O₂           → CO₂

2H₂ + O₂          → 2H₂O

08. Reversible Reaction: - When a chemical reaction is possible in both sides (forward and backward) at the same time is known as reversible reaction. It is shown with sign of reversibility . It is completed into two phases.

a) Forward Reaction: - When reaction took place in forward direction it is known as forward reaction 

N₂(g) + 3H₂ (g) → 2NH₃

b) Backward Reaction: - When reaction took place in backward direction it is known as backward reaction. It is the Reverse Reaction of the forward reaction.

2NH₃(g) → N₂(g)+3H₂(g)

Both reactions in single form is written as

 09. Photo Chemicals Reaction: - Reactions completed into the sunlight is known as photochemical reaction for exe Photography and photosynthesis.

In Photosynthesis the following reaction completed.

                        Sun Light

6CO₂ + 12H₂O→ C₆H₁₂O₆ + 6H₂O +6O₂

                   Chlorophyll

Average Reaction Rate : -  The Rate of reaction measured by observing the change for a long time interval is know as Average Reaction Rate.

Instantaneous Reaction Rate : - When rate of reaction is measured in a given time is called Instantaneous Reaction Rate.

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[1] Chemical Properties – Heat of combustion, reactivity with water, PH, and electromotive force, Toxicity

Physical Properties –  brittleness, opacity, luster, boiling point, melting point, color, concentration, density, ductility, hardness, elasticity, plasticity, electric charge, electrical conductivity, flow rate, fluidity, intensity, luminance, malleability, permeability, resistivity, solubility, specific heat, temperature, tension, pressure

[2] Burning, Respiration and Rottening or decomposing are also Exothermic reaction.

[3]

[4]* AgCl is White in colour but Ag is in brown in silvery.