Solutions of Chemical Reactions and Equations (Page No - 19) - Chemistry Lakhmir Singh, Class 10 PDF Download

Question 12:
Complete and balance the following equations :
(a) NaOH + ………… —–> Na₂S0₄ + H₂0
(b) Ca(OH)₂ + ……….—–> CaC0₃ + H₂0
Solution :
(a) 2NaOH + H₂SO₄ —–> Na₂SO₄ + 2H₂O
(b) Ca(OH)₂ + CO₂ —–> CaCO₃ + H₂O

Question 13:
Correct and balance the following equations :

1. Ca + H₂0 — > CaOH + H
2. N + H — > NH₃

Solution :

1. Ca + 2H₂O —–> Ca(OH)₂ + H₂
2. N₂ + 3H₂ —–> 2NH₃

Question 14:
Write complete balanced equations for the following reactions :
(a) Calcium (solid) + Water (liquid) —–> Calcium hydroxide (solution) + Hydrogen (gas)
(b) Sulphur dioxide (gas) + Oxygen (gas) —–> Sulphur trioxide (gas)
Solution :
(a) Ca (s) + 2H₂O(l) —–> Ca(OH)₂(aq) + H₂ (g)
(b) 2SO₂(g) + O₂ (g) —–> 2SO₃(g)

Question 15:

1. Na + O₂ —–> Na₂O
2. H₂O₂ —–> H2O + O₂
   
3. Mg(OH)₂+ HCl —–> MgCl₂ + H₂O.
4. Fe + O₂ —–> Fe₂O₃
5. Al(OH)₃ —–> Al₂O₃ + H₂O
6. NH₃+ CuO —–> Cu + N₂ + H₂O
7. Al₂(SO₄)₃+ NaOH —–> Al(OH)₃ + Na₂SO₄
8. HNO₃+ Ca(OH)₂ —–> Ca(NO₃)₂ + H₂O
9. NaOH + H₂SO₄ —–> Na₂SO₄ + H₂O
10. BaCl₂+ H₂SO₄ —–> BaSO₄ + HCl

Solution :

1. 4Na + O₂ —–> 2Na₂O
2. 2H₂O₂ —–> 2H₂O + O₂
3. Mg(OH)₂+ 2HCl —–> MgCl₂ + 2H₂O.
4. 4Fe + 3O₂ —–> 2Fe₂O₃
5. 2Al(OH)₃ —–> Al₂O₃ + 3H₂O
6. 2NH₃+ 3CuO —–> 3Cu + N₂ + 3H₂O
7. Al₂(SO₄)₃+ 6NaOH —–> 2Al(OH)₃ + 3Na₂SO₄
8. 2HNO₃+ Ca(OH)₂ —–> Ca(NO₃)₂ + 2H₂O
9. 2NaOH + H₂SO₄ —–> Na₂SO₄ + 2H₂O
10. BaCl₂+ H₂SO₄ —–> BaSO₄ + 2HCl

Question 16:
Fill in the following blanks with suitable words :
(a) Chemical equations are balanced to satisfy the law of…….
(b) A solution made in water is known as an………. solution and indicated by the symbol…………….
Solution :
(a) Conservation of mass
(b) Aqueous; (aq)

Question 17:
(a) Give one example of a chemical reaction.
(b) State two characteristics of the chemical reaction which takes place when dilute sulphuric acid is poured over zinc granules.
(c) Give two characteristics of the chemical reaction which occurs on adding potassium iodide solution to lead nitrate solution.
Solution :
(a) Magnesium Ribbon is heated in the presence of air to form a white powder called magnesium oxide.
(b) When dilute sulphuric acid is poured over zinc granules

1. there will be a rise in temperature
2. evolution of hydrogen gas.

(c) A yellow precipitate is formed.

1. There will be a change in color (from colourless to yellow).

Question 18:
(a) What is a chemical equation ? Explain with the help of an example.
(b) Giving examples, state the difference between balanced and unbalanced chemical equations.
(c) Balance the following chemical equations :

1. NH₃  —–> N₂ + H₂
2. C +C0₂ —–> CO

Solution :
(a) The method of representing a chemical reaction with the help of symbols and formulae of substances involved in it is called a chemical equation.
Example: Zinc metal reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas. This equation is written as: Zn + H₂SO₄ —–> ZnSO₄ + H₂
(b) A balanced chemical equation has an equal number of atoms of different elements in the reactants and products. It has equal masses of various elements in the reactants and products.
Example: Zn + H₂SO₄ —–> ZnSO₄ + H₂
An unbalanced chemical equation has an unequal number of atoms of one or more elements in the reactants and products. It has unequal masses of various elements in the reactants and products.
Example: H₂ + O₂ —–> 2H₂O
(c) 2NH₃ —–> N₂ + 3H₂

1. C + CO₂ —–> 2CO

Question 19:
When hydrogen is passed over copper oxide, copper and steam are formed. Write a balanced equation for this reaction and state which of the chemicals are :

1. elements
2. compounds
3. reactants
4. products
5. metals
6. non-metals

Solution :
H₂ + CuO —–> Cu + H₂O

1. Elements : H2 and Cu
2. Compounds : CuO and H2O
3. Reactants: H2 and CuO
4. Products: Cu
5. Metal: Cu
6. Non-metal: H₂

Question 20:
(a) What are the various ways in which a chemical equation can be made more informative ? Give examples to illustrate your answer.
(b) Write balanced chemical equation from the following information :
An aqueous calcium hydroxide solution (lime water) reacts with carbon dioxide gas to produce a solid calcium carbonate precipitate and water.
Solution :
(a) The various ways in which a chemical equation can be made more informative are :
(i) By indicating the physical states of the reactants and products. Example: Gaseous state is indicated by the symbol (g).
Zn (s) + H₂SO₄ (aq) —–> ZnSO₄ (aq) + H₂ (g)
(ii) By indicating the heat changes taking place in the reaction. For xxample: An exothermic reaction is indicated by writing “+Heat” or “+Heat energy” or “+Energy” on the products side of an equation.
C (s) + O₂ (g) —–> CO₂ (g) + Heat
(iii) By indicating the “conditions” under which the reaction takes place.
Example: Delta stands for heat which is written over the arrow of the equation.

(b) Ca(OH)₂ (aq) + CO₂ (g) —–> CaCO₃ (s) + H₂O (l)

Question 21:
(a) What is a balanced chemical equation ? Why should chemical equations be balanced ?
(b) Aluminium burns in chlorine to form aluminium chloride (AlCl₃). Write a balanced chemical equation for this reaction.
(c) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas. Write a balanced chemical equation for this reaction.
Solution :
(a) A balanced chemical equation has an equal number of atoms of different elements in the reactants and products. It has equal masses of various elements in the reactants and products. A chemical equation should be balanced to satisfy the law of conservation of chemical reactions.
(b) 2Al + 3Cl₂ —–> 2AlCl₃
(c) 2K + 2H₂O —–> 2KOH + H₂