Chapter - 1
Chemical Reactions and Equations
Points to remember:-
1. A chemical equation represents a chemical reaction occurring in a chemical change. It is a symbolic representation of a chemical reactions presented with the help of symbols of elements and molecular formulae/chemical formulae of comounds.
2. A chemical equation is balanced so that the number of atoms of each element involved in a chemical reaction are the same on the reactant and product sides of the equation. It is required to balance a chemical equation because a chemical equation represents a chemical reaction and in the course of a chemical reaction the law of conservation of mass (given by A. Lavoisier) is followed. It must be noted no matter is created or destroyed in the course of a chemical reaction.
3. Combination reaction:- The reaction in which two or more substances combine to form a new single substance.
4. Decomposition reaction:- The reaction in which a single substance decomposes to give two or more substances. It can be thermal (by heat) or electrolytic (by electric current) decomposition or photolytic (by sunlight).
5. Displacement reaction:- The chemical reaction in which an element displaces another
element from its compound. Note: A more reactive metal displaces a less reactive metal from its compound.
6. Double displacement reaction:- The reaction in which two different atoms or group of
atoms (ions) are mutually exchanged. Precipitation reactions and neutralization reactions are its great examples.
7. Precipitation reaction:- The reaction that produces insoluble salts on mixing two clear solutions. E.g. When a solution of Sodium sulphate is mixed with a solution of Barium chloride, a white precipitate of Barium sulphate is produced.
8. Oxidation is the gain of oxygen or loss of hydrogen.
9. Reduction is the loss of oxygen or gain of hydrogen.
10. Redox reaction:- The reaction in which one reactant gets oxidised while the other gets reduced. Oxidation and Reduction do not take place in isolation. They do occur simultaneously.
11. Exothermic reaction:- Reaction in which heat is given out along with the products. As a result of this reaction, the temperature of the reaction system rises and we can feel that the test tube containing the reaction mixture has become hotter.
12. Endothermic reaction:- Reaction in which energy is absorbed by the reactants. As a result of this reaction the temperature of the reaction system falls.
13. Corrosion:- When a metal is attacked by substances around it such as moisture, acids etc. it is said to corrode and this process is called corrosion. Rusting of iron is common example of corrosion. In rusting of Iron, Iron reacts with moisture and oxygen present in air in presence of acidic substances as CO2 to form a brown coloured loose flaky substance, known as rust.
14. Rancidity:- When fats and oils are oxidised, they become rancid and their smell and
taste change. In order to prevent rancidity, we must add antioxidants to the food items and store them under refrigeration system.
Class : X Chemistry Some model Questions from the Chapter: Chemical Reactions
QUESTIONS
1 mark questions:-
1. What change do you observe, when magnesium ribbon is burnt in air?
2. Define decomposition.
3. Name the chemical reaction in which heat is absorbed.
4. Name the type of reaction in which two or more substances combine to form a new
single product.
5. What is Redox reaction?
6. What happens when electric current is passed through acidified water?
7. Define corrosion.
8. Name one metal which does not corrode.
9. Define Rancidity.
10. Which type of chemical reaction takes place when Barium hydroxide and ammonium chloride, are mixed together in terms of heat released or absorbed?
11. Name the type of reaction taking place when iron nails are dipped in copper sulphate solution.
12.Name the group of chemical substances used to prevent oxidation.
13. Write one disadvantage of corrosion of metals.
14. Give one disadvantage of oxidation in our daily life?
2 marks questions:-
15. What is balanced chemical equation? Why should a skeletal equation is to be balanced?
16. What information regarding physical state do you get from the following notations – (g), (l), (aq) and (s)?
17. Arrange Iron, Zinc and Copper in increasing order of reactivity from the following reactions:-
18. Define combination reaction. Give one example of a combination reaction which is also exothermic.
19. When lead nitrate powder is heated. Mention the name and colour of the gas evolved?
20. With the help of suitable example explain Oxidation and Reduction in terms of gain or loss of oxygen.
21. Write two methods by which oxidation process of food can be slowed down at home.
22. What happens when a strip of zinc is dipped into a solution of copper sulphate? Write the balanced chemical equation of the reaction.
23. Translate the given statement, first in word equation and then into skeletal equation:-
Solutions of barium chloride and sodium sulphate in water reacts to give insoluble
barium sulphate and the solution of sodium chloride.
24. Oil and fat containing food items (Chips) are flushed with Nitrogen. Give reason.
25. Respiration is considered an exothermic reaction. Explain why?
3 marks questions:-
26. Define displacement reaction. Give one example of it. How is it different from double
displacement reaction.
27. Define decomposition reactions. Give one example each of thermal decomposition and
electrolytic decomposition.
28. For the following equation:-
Heat
Pb (NO3 )2 (s) ⎯⎯⎯→PbO(s) + NO2 (g) + O2 (g)
(i) Write name and colour of the precipitate formed.
(ii) Balance the above chemical equation.
(iii) Name the type of chemical reaction.
29. Write the balanced chemical equations for the following reactions:-
(i) Barium chloride + Potassium sulphate →Barium sulphate + Potassium chloride
(ii) Sodium chloride + Silver nitrate →Silver chloride + Sodium nitrate.
(iii) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water.
30. Identify the substances that are oxidised and the substances that are reduced in the
following reactions:-
(i) ZnO + C →Zn + CO
(ii) CuO + H2 → Cu + H2O
31. Balance the following equations and state whether they are exothermic or endothermic:-
(i) Na + H2O → NaOH + H2+ heat
32. Name the type of chemical reaction represented by the following equations :–
5 marks questions:-
33. Name the type of chemical reactions taking place when:-
(i) Lime stone is heated.
(ii) Magnesium ribbon is burnt in air.
(iii) Iron nails are dipped in copper sulphate solution.
(iv) Burning of coal.
(v) Sodium sulphate is mixed with barium chloride.
34. Balance the following chemical reactions and state the type of chemical reactions:-
(i) Electrolysis
H2O ⎯⎯⎯⎯→H2 + O2
(ii) CaO + H2O → Ca(OH) 2
(iii) Heat
CuO + H2 ⎯⎯⎯→Cu + H2O
35. Translate the following statements into chemical equations and balance them :-
(i) Sodium chloride reacts with silver nitrate to give sodium nitrate and a precipitate of
silver chloride.
(ii) Hydrogen gas combines with nitrogen to form ammonia.
(iii) Zinc carbonate decomposes to give zinc oxide and carbon dioxide.
(vi) Ammonia gas reacts with water to give ammonium hydroxide.
(v) Copper (II) oxide on heating with hydrogen gas gives copper and water.
36. In the reaction represented by the equation
Balance the equation and identify :–
(a) Substance oxidised
(b) the substance reduced
(c) the oxidising agent
(d) the reducing agent
37. Name the types of reactions involved :–
(a) burning of Methane gas
(b) decomposition of vegetable matter into compost.
(c) Heating of Ferrous sulphate.
(d) exposure of silver bromide to sunlight
(e) Heating of copper powder in air.
38. (i) Write any two informations conveyed by a balanced chemical equation.
(ii) State the steps involved in balancing a chemical equation.
(iii) Sodium metal reacts with water to give sodium hydroxide and hydrogen.
Translate the statement into chemical equation and then balance.
(iv) Why are decomposition reactions called opposite of the combination reactions (any
one reason)
(v) Why magnesium ribbon is cleaned with the help of sand paper before use?
39.Explain with suitable reasons :– (Write chemical equation also)
(a) Silver bromide is become kept in dark coloured (brown coloured bottles)
(b) Iron nails become brownish and then blue in colour when kept in copper sulphate
solution.
(c) Sodium sulphate reacts with barium chloride solution, a precipitation reaction takes
place.
(d) Calcium oxide reacts vigorously with water to form slaked lime.
(e) Carbohydrates broken down to form glucose combine with oxygen in cell provide
energy.
