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 :
Solution :
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:
Solution :
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
(c) A yellow precipitate is formed.
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 :
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
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 :
Solution :
H2 + CuO —–> Cu + H2O
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
1. What is a chemical reaction? |
2. How can chemical reactions be represented? |
3. What is the importance of balancing chemical equations? |
4. How do you balance chemical equations? |
5. What are the different types of chemical reactions? |
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