"AKC SCIENCE CLASSES"
CLASS 10 TH (CBSE AND MP BOARD)
CHAPTER 10
Chemical Reactions and Equations
Basic Concepts
1) Chemical reactions takes place are represented by fully balanced chemical equations, i.e., the number of atoms of each type involved in a reaction are the same on the reactant and product side of the chemical equations.
2) A simple equation is balanced by hit and trial method so that same total number of charges and atoms appear on both sides of the equation. For example when iron combines with steam to form FeO and H, it is balanced in the form following steps :-
(ⅰ) Fe + H₂O → Fe₃O₄ + H₂ (Skeletal equation)
(ⅱ) Fe + 4H₂O → Fe₃O₄ + H₂ (O is made equal on both sides)
(ⅲ) Fe + 4H₂O → Fe₃O₄ + 4H₂ (H is made equal on both sides)
(ⅳ) 3Fe + 4H₂O → Fe₃O₄ + 4H₂ (Fe is made equal on both sides)
This balanced equation
Right Left
Fe 3 3
O 4 4
H 8 8
If the reaction is complicated i.e., it involves large number of reactants and products, it is written in steps which are balanced as above and then added up to get the final reactants and products. This is called partial equation method.
3) A complete chemical equation gives the formulae of the reactants and products, their physical states and brief conditions under which a reaction occurs.
4) There are several types of reactions. These involve breaking of bonds and formation of new ones by the effect of heat, light or mechanical shaking.
- A decomposition reaction occurs when a compound is broken into smaller parts. It may be either thermal decomposition or electrolytic decomposition or light decomposition.
- In combination reaction, two or more substances combine to form a new substance.
- The reaction in which an atom or group of atoms in a molecule is replaced by another atom or group of atoms is called displacement reaction. When two reacting molecules exchange their partner ions in solution, it will be double displacement reaction.
- It is said to be a dissociation reaction, when a substance breaks up into its ions.
- In precipitation reactions, insoluble salts are formed.
- In redox reactions, a substance gains oxygen or loses hydrogen, i.e., gets oxidised and simultaneously, another substance loses oxygen or gains hydrogen, i.e., gets reduced.
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INTEXT QUESTIONS AND ANSWERS
NCERT INTEXT QUESTIONS (PAGE NO:- 06)
Q.01:- Why should a magnesium ribbon be cleaned before burning in air?
Ans:- Magnesium ribbon should be cleaned before burning in air so that unwanted impurities are removed and we burn only pure magnesium metal.
Q.02:- 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 → HCl
H₂ + Cl₂ → 2HCl
(ⅱ) BaCl₂ + Al₂(SO₄)₃ → BaSO₄ + AlCl₃
3BaCl + Al₂(SO₄)₃ → 3BaSO₄ + 2AlCl₃
(ⅲ) Na + H₂O → NaOH + H₂
2Na + 2H₂O → 2NaOH + H₂
Q.03:- Write a balanced chemical equation with state symbols for the following reactions :-
(ⅰ) Solution of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(ⅱ) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
Ans:- (ⅰ) BaCl₂(aq) + Na₂SO₄ (aq) → BaSO₄ (s) + 2NaCl(aq)
(ⅱ) NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O
NCERT INTEXT QUESTIONS (PAGE NO:- 10)
Q.01:- 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) 'X' is quick lime, CaO.
(ⅱ) CaO(s) + H₂O → Ca(OH)₂(aq)
quick lime slaked lime
or
Calcium hydroxide
Q.02:- Why is the amount of gas collected in one of the test tubes in Activity 1.7 [Text book] double of the amount collected in the other?
Ans:- In Activity (1.7) water is electrolysed to give H₂ gas at one electrode and O₂ gas at the other electrode according to the given chemical reaction :-
2H₂O(l) → 2H₂(g) + O₂(g)
Thus two molecules of water on electrolysis to give 2 molecules of hydrogen gas and one molecule of oxygen gas or the amount of hydrogen gas collected would be double than that of oxygen gas.
NCERT INTEXT QUESTIONS (PAGE NO:- 13)
Q.01:- Why does the color of copper sulphate solution change when an iron nail is dipped in it?
Ans:- When an iron nail is dipped in copper sulphate solution, it becomes brownish in color and color of copper sulphate fades due to the following reaction :-
Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
Copper
Sulphate
In this reaction iron has replaced copper from its solution. Thus, amount of copper from its solution. Thus, amount of copper sulphate decreases and its color fades.
Q.02:- Give an example of a double displacement reaction other than the one given in Activity 1.10.
Ans:- When a solution of hydrochloric acid is added to a solution of lead nitrate, a white precipitate of lead chloride is formed.
Pb(NO₃)₂(aq) + 2HCl → PbCl₂(s) + 2HNO₃(aq)
Lead Nitrate Lead chloride
Pb⁺⁺ ions from lead nitrate combine with 2Cl⁻ ions from hydrochloric acid and a precipitate of lead chloride is formed. Thus, there is an exchange of ions between the two reactants i.e., lead nitrate and hydrochloric acid, and thus this reaction is a double displacement reaction.
Q.03:- Identify the substances that are oxidised and the substances that are reduced in the following reactions :-
(ⅰ) 4Na(s) + O₂(g) → 2Na₂O(s)
(ⅱ) CuO(s) + H₂(g) → Cu(s) + H₂O(l)
Ans:- (ⅰ) Substance oxidised :- Cu(s), H₂(g)
(ⅱ) Substance reduce :- O₂(g), CuO(s).
CHAPTER :- 01 || EXERCISE QUESTIONS AND ANSWERS CLICK HERE
