CBSE Class 10 Chemistry Chemical Reactions And Equations Worksheet Set D

Question : Why decomposition reactions are called the opposite of combination reactions? Write equations for these reactions.
Answer :  A decomposition reaction may be defined as the reaction in which a single substance decomposes or splits into two or more substances under suitable conditions.
For example,

Question :   Identify the type of reaction in the following examples :
(i) Na₂SO₄(aq) + BaCl₂(aq) ———-> BaSO₄(s) + 2NaCl(aq)
(ii) Fe(s) + CuSO₄(aq) ———-> FeSO₄(aq) + Cu(s)
(iii) 2H₂(g) + O₂(g) ———> 2H₂O(l)
Answer :
(i) It is an example of double displacement reaction.
(ii) It is an example of displacement reaction.
(iii) It is an example of combination reaction.

Question : When Hydrogen gas is passed over heated copper (II) oxide, copper and steam are formed. Write the balanced chemical equation with physical states for this reaction. State what kind of chemical reaction is this?
Answer :

This is a Redox reaction.

Question : Define a combination reaction. Give one example of a combination reaction which is also exothermic.
Answer :   A combination reaction is said to have occurred when two or more than two substances combine to form a single substance.

Question : Name and state the law which is kept in mind while we balance a chemical equation.
Answer :   Law of conservation of mass. Mass can neither be created nor be destroyed during a chemical reaction.

Question :   Which of the following statements about the given reaction are correct?
3Fe (s) + 4H₂O (g) → Fe₃O₄ (s) + 4 H₂ (g)
(i) Iron metal is getting oxidized
(ii) Water is getting reduced
(iii) Water is acting as reducing agent
(iv) Water is acting as oxidizing agent
(a) (i), (ii) and (iii)
(b) (ii) and (iv)
(c) (i), (ii) and (iv)
(d) (ii) and (iv)
Answer: C

Question : Oxidation is a process which involves
(i) addition of oxygen
(ii) addition of hydrogen
(iii) removal of oxygen
(iv) removal of hydrogen
a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)
Answer : C

Question :
(a) Why cannot a chemical change be normally reversed?
(b) Why is it always essential to balance a chemical equation?
(c) Why do diamond and graphite, the two allotropic forms of carbon evolve different amounts of heats on combustion?
(d) Can rusting of iron take place in distilled water?
Answer :
(a) In a chemical change, the products are quite different from the reactants. Therefore, it cannot be normally reversed.
(b) A chemical equation has to be balanced to meet the requirement of the law of conservation of mass. According to the law, the total mass of the reacting species taking part in the reaction is the same as that of the products formed. Since there is a direct relationship between the mass of the different species and their number, it is always essential to balance a chemical equation.
(c) Because they differ in the arrangement of carbon atoms present and have different shapes. The attractive forces among the atoms in the two cases are not same. That is why they evolve different amount of heat.
C(diamond) + O₂(g) ———–> CO₂(g) + 393.5 kj
C(graphite) + O₂(g) ———–> CO₂(g) + 395.4 kj
Please note that diamond and graphite are the two allotropic forms of carbon.
(d) No, rusting of iron cannot take place in distilled water because it neither contains dissolved oxygen nor carbon dioxide. Both are essential for the rusting of iron.

Question :   A silvery white metal X is in the form of ribbons. Upon ignition, it burns with a dazzling white flame to form white powder Y. When water is added to the powder Y, it partially dissolves to form a substance Z which is used as an antacid.
(a) What is metal X?
(b) Name the white powder Y.
(c) What is the substance Z ?
(d) Write the chemical reactions that are taking place.
Answer :
(a) The metal is X is Mg.
(b) The white powder Y is MgO.
(c) White powder Y dissolves partially in water to form substance Z. It is Mg (OH), and is used as an antacid.
(d) The chemical reactions that are taking place are :

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