NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations includes all the important topics with detailed explanation that aims to help students to understand the concepts better. Question 1 Why should a magnesium ribbon be cleaned before burning in air? Answer: Magnesium gets covered with a layer of magnesium oxide when kept in air for a long time.
This layer hinders the burning of magnesium. Hence, it is to be cleaned before burning. Question 2 Write the balanced equation for the following chemical reactions. Question 3 Write a balanced chemical equation with state symbols for the following reactions : i Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
Answer: i The substance whose solution in water is used for white washing is calcium oxide or quick lime. Its formula is CaO.
Question 2 Why is the amount of gas collected in one of the test tubes in text book Activity 1. Name this gas. Question 1 Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
OR An iron nail is dipped in the solution of copper sulphate for about 30 minutes. State the change in colour observed. Give reason for the change.
The colour of copper sulphate solution fades due to the formation of light green solution of iron sulphate. Question 2 Give an example of a double displacement reaction other than the one given in Activity 1. Answer: Sodium hydroxide and hydrochloric acid react to form sodium chloride and water. Question 3 Identify the substances that are oxidised and the substances which are reduced in the following reactions.
Question 1 Which of the statements about the reaction below are incorrect? Question 3 What happens when dilute hydrochloric acid is added to iron filings? Tick the correct answer : a Hydrogen gas and iron chloride are produced.
Answer: a Hydrogen gas and iron chloride are produced. Question 4 What is a balanced chemical equation? Why should chemical equations be balanced? Answer: A balanced chemical equation has an equal number of atoms of different elements in the reactants and products.
The chemical equations should be balanced to satisfy the law of conservation of mass. Question 5 Translate the following statements into chemical equations and then balance them.
Question 9 What does one mean by exothermic and endothermic reactions? Give examples. Answer: Exothermic reactions : Those reactions in which heat is evolved are known as exothermic reactions. Endothermic reactions : Those reactions in which heat is absorbed are known as endothermic reactions.
Question 10 Why is respiration considered an exothermic reaction? Answer: Respiration is an exothermic process because during respiration glucose combines with oxygen in the cells of our body to form carbon dioxide and water along with the production of energy. Question 11 Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions. Answer: In a decomposition reaction, a single compound breaks down to produce two or more simpler substances.
For example:. While, in a combination reaction, two or more substances simply combine to form a new substance. Question 12 Write one equation each for the decomposition reactions where energy is supplied in the form of heat, light or electricity. OR Decomposition reactions require energy either in the form of heat or light or electricity for breaking down the reactants.
Write one equation each for decomposition reactions where energy is supplied in the form of heat, light and electricity. Question 13 What is the difference between displacement and double displacement reactions? Answer: In displacement reactions, a more reactive metal displaces a less reactive metal from its solution. In double displacement reactions, two reactants in solution exchange their ions. Question 14 In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal.
Write down the reaction involved. Question 15 What do you mean by a precipitation reaction? Explain by giving examples. Answer: A reaction in which an insoluble solid called precipitate is formed that separates from the solution is called a precipitation reaction.
Question 16 Explain the following in terms of gain or loss of oxygen with two examples each: a Oxidation and b Reduction. Answer: a Oxidation : The addition of oxygen to a substance is called oxidation. The black coloured compound is copper oxide CuO. The reaction involved is.
Question 18 Why do we apply paint on iron articles? Answer: Paint does not allow iron articles to come in contact with air, water and saves iron articles from damage due to rusting.
Question 19 Oil and fat containing food items are flushed with nitrogen. Answer: To keep food items fresh and save from getting oxidised, food items are flushed with nitrogen. Question 20 Explain the following terms with one example each a Corrosion, b Rancidity. Answer: a Corrosion : It is the process in which metals are eaten up gradually by the action of air, moisture or a chemical such as an acid on their surface.
Example : When iron is exposed to moist air for a long period of time, its surface acquires a coating of a brown, flaky substance called rust. Rancidity spoils the food materials prepared in fats and oils which have been kept for a considerable time and makes them unfit for eating. Rancidity can be prevented by adding anti-oxidants to foods containing fats and oils. It can also be prevented by flushing fat and oil containing foods with nitrogen before sealing.
Question 1 Which of the given statements about the reaction below are incorrect? Lead is getting reduced b. Carbon dioxide is getting oxidised c. Carbon is getting oxidised d. Lead oxide is getting reduced i a and b ii a and c iii a , b and c iv all Solution: i a and b. Question 2 The above reaction is an example of a i. Combination reaction ii. Double displacement reaction iii. Decomposition reaction iv. Displacement reaction Solution: iv Displacement reaction.
Question 3 What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer. Hydrogen gas and iron chloride are produced b. Chlorine gas and iron hydroxide are produced c. No reaction takes place d Iron salt and water are produced Solution: Hydrogen gas and iron chloride are produced. Solution: An equation for a chemical reaction is an equation in which the number of atoms for each element in the reaction and the total charge is the same for both the reactants and the products.
In other words, the mass and the charge are balanced on both sides of the reaction. Hydrogen gas combines with nitrogen to form ammonia b. Hydrogen sulfide gas burns in air to give water and sulfur dioxide c. Barium chloride reacts with Aluminium sulfate to give Aluminium chloride and a precipitate of barium sulphate d. Potassium metal reacts with water to give a potassium hydroxide and hydrogen gas Solution: a.
Question 6 Balance the following chemical equations. Question 8 Write the balanced chemical equation for the following and identify the type of reaction of each case. Solution: a. Question 9 What is meant by exothermic and endothermic reactions? Solution: An exothermic reaction is one that releases heat.
If 1 mole of N 2 molecule reacts with 1 mole of O 2 molecule, the heat of KJ has to be supplied to initiate the reaction to give 1 mole of NO molecule. This means that the bonds between N � N and O � O are so strong that they do not break easily. N 2 has triple covalent bond between the two N atoms. O 2 has a double covalent bond. Thus energy has to be put into the reaction to break the strong bonds.
Thus the above reaction is a good example of an endothermic reaction. Solution: During respiration, glucose combines with oxygen in the cells of our body to form carbon dioxide and water along with the production of energy. Write equations for decomposition reactions. Solution: Essentially, decomposition reactions are the opposite of combination reactions.
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