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NCERT Book Notes for Class 10th, Answers to Intext Questions All the questions and answers related to this lesson have been explained in detail. We will answer every question related to you.
Lesson 1. Chemical Reaction That Equation
** Chemical Reaction :-
When a chemical change occurs in any substance, it is called a chemical reaction.
Let us take an example to understand a chemical reaction.
1. First you wrap a magnesium
ribbon Scrub it clean with
sandpaper.
2. Now hold it with a tong and
remove it from the burner.
Burn it.
3. Put the magnesium ash in a glass.
The ashes you put in a glass glass. It is white, but the reason behind it being white is oxygen, when you combust it, there is a chemical reaction between the oxygen present in the air and magnesium. Due to this action, its powder / ash is white. We call this powder magnesium oxide.
This is a chemical reaction, now you must have understood it. But if you still don't understand, let us take an example.
1. Take a test tube.
2. Add a small amount of zinc to it.
3. Now add dilute hydrochloric acid
or sulfuric acid to it.
4. Did you see any change?
5. You touch the test tube to see if
there was any effect on its
temperature.
If there is a change in the state of a substance, a change in colour, ejection/emission of a gas or a change in temperature, etc. Stages can be understood as a chemical reaction.
Types of Chemical Reaction:-
1. combination reaction;
2. exothermic reaction;
3. dissociation reaction;
4. displacement reaction;
5. double displacement reaction;
6. redox reaction;
1. Combination Reaction
Chemical reactions in which two or more reactants (substances) combine to form a single product. are called combination reactions.
like:
In this reaction, molecules of solid calcium oxide and water are joined to form the single product calcium hydroxide. Calcium oxide is slaked lime. Which is used for whitewashing the walls.
Two or three days after the calcium hydroxide produced in the above chemical reaction whitens the walls, it reacts slowly with CO2 to form calcium carbonate, also known as marble.
2. Decomposition reaction
Chemical reactions in which a single reactant (compound) breaks down to form two or more products are called decomposition or decomposition reactions.
Decomposition reactions involve the absorption of heat, hence they are also called endothermic reactions. it has three forms
1. heat
2. Heating
3. Electricity
3. Displacement reaction
Chemical reactions in which one element separates another element from its compound are called displacement reactions.
like:
When an iron nail is placed in a solution of copper sulphate, the color of the nail becomes brown, the color of the solution of copper sulphate turns blue. Because iron separates copper from its solution.
4. Double displacement reaction
The chemical reactions in which there is an exchange of ions between the reacting agents and all the reactions are called double displacement reactions.
In this reaction, a precipitate of BaSO4 is formed by the action of Ba2+ and (SO4)2- ions.
5. Oxidation and Reduction
The chemical reactions in which one reactant is oxidised and another reactant is reduced are called oxidation-reduction (redox) reactions.
Addition of oxygen or removal of hydrogen to the reactant is called oxidation and the release of oxygen or addition of hydrogen is called reduction.
like:
On heating of this chemical reaction, copper is reduced and hydrogen is oxidised.
6. exothermic reaction
All those chemical reactions in which heat is also released along with the formation of products are called exothermic reactions.
such as the combustion of natural gas.
7. endothermic reaction
All those chemical reactions in which heat is absorbed are called endothermic reactions.
All decomposition reactions
Effects of oxidation reactions in our daily life:
1. Corrosion
2. Tooth odor
1. Corrosion
When a metal comes in contact with acid, alkali, moisture etc., it starts getting destroyed which is called corrosion.
Due to corrosion, a black layer on top of silver and a green layer on top of copper.
It is due to corrosion that bridges, iron railings, ships, metals, especially objects made of iron, get destroyed.
The main reason for this is the oxidation reaction.
Corrosion can be prevented by panting.
2. Tooth odor
When fatty or oily food items are stored for a long time, they are oxidised, due to which their taste and smell change and they become foul-smelling, food items are kept in airtight containers to prevent its effects .
Chip makers remove oxygen from the bag of chips and fill it with a less active gas like nitrogen so that they cannot be oxidized.
Why is magnesium ribbon cleaned before burning in air?
**Textual Question Answer:-
1. Before burning in air, magnesium ribbon is cleaned with sandpaper, which removes the impurities accumulated on it and it is easily combusted, so magnesium ribbon is cleaned before burning in air.
2. What is Hit and Trial?
While balancing a chemical equation, the coefficients written are repeatedly written and erased until the equation is balanced, this method of balancing the equation is called hit and trial method.
3. Hydrogen + Chlorine → Hydrogen Chloride Chemical Reaction
H2 + Cl2 → 2HCl (Combination Reaction)
Hydrogen + Chlorine → Hydrogen Chloride Chemical Reaction
H2 + Cl2 → 2HCl (Combination Reaction)
4. How is respiration an exothermic reaction?
Animals need energy to survive, which is present in food, due to the decomposition of carbohydrates present in food, glucose is formed, which reacts with oxygen present in the cells to generate energy, so energy is being generated in this reaction. Hence respiration is an exothermic reaction. Its equation is as follows:-
C6 H12 O6 + 6O2 → 6CO2 + 6H2O + energy.
The decomposition of vegetable vegetables (vegetables) into compost is also an example of exothermic reaction.
5. What will be the reaction when a copper wire is dipped in a solution of iron sulphate?
No reaction will take place because copper is less reactive than iron.
6. What is the name of the reducing substance in the following reaction?
2PbO + C → 2Pb + CO2
The reducing substance in this reaction is carbon, because it takes oxygen from PbO and reduces it.
7. Which type of reaction is the following?
Fe2O3 + 2Al → Al2O3 + 2Fe
displacement reaction.
8. Name any one antioxidative substance used to prevent rancidity of food items?
Antioxidant called BHA (butylated hydroxy-anisole).
9. What is the reason for silver coating on silver and green on copper if kept for a long time?
Due to corrosion of oxidation reaction.
10. The reaction in which one substance is oxidised and the other is reduced is called?
Redox reaction or oxidation-reduction reaction.
11. Why is the amount of hydrogen obtained by electrolysis of water twice that of oxygen?
The amount of hydrogen obtained by electrolysis of water is twice that of oxygen because water (H2O) is made up of two parts of hydrogen and one part of oxygen.
12. What happens when dilute hydrochloric acid is added to iron powder?
Hydrogen gas and iron chloride are formed when dilute hydrochloric acid is added to iron powder.
Fe + 2HCl → FeCl2 + H2
13. Give an example explaining the meaning of chemical reaction?
Chemical reactions are those processes in which new substances with new properties are formed. The substances which take part in a chemical reaction are called reactants and the new substances which are formed in a chemical reaction are called products.
When Mg tape is burnt in air, it reacts with the oxygen present in the air to form a white powder of magnesium oxide.
14. Explain the characteristics of chemical reactions.
The following are the characteristics of chemical reactions:-
The release of gas, the formation of a precipitate, the change in color, change in temperature, change in state are the symptoms of chemical reactions.
15. Why should a magnesium tape be rubbed and cleaned before burning it in air?
Before burning the Mg tape in air, it is rubbed with a rag because the action of moist air on the Mg tape forms a layer of basic magnesium carbonate [MgCO3 + Mg(OH)2], due to which the oxygen of the air is tried to be burnt. This layer of basic magnesium carbonate is cleaned by rubbing it with sandpaper.
16. What is a chemical equation? Why does a chemical equation have to be balanced?
When a chemical reaction is represented with the help of symbols and formulas of the substances involved, it is called a chemical equation. Chemical equations are written between reactants and products by placing an arrow (→) from the reactant to the product.
The equations are balanced because matter can neither be created nor destroyed according to the law of conservation of mass. This means that the total mass of all the reactants must necessarily be equal to the total mass of the products. For this reason the number of different atoms on both sides of the equation is equalized.
17. What do you understand by endothermic and exothermic reactions? Explain with example?
1. Endothermic Reactions :-
The reactions in which heat is absorbed are called endothermic reactions. All decomposition reactions are endothermic reactions.
CaCO3 + heat → CaO + CO2 (thermal decomposition of calcium carbonate)
2. Exothermic reaction-
The reactions in which heat is released are called exothermic reactions. All combustion reactions are exothermic reactions.
Mg + O2 → 2 MgO + heat (combustion of magnesium)
18. Respiration is considered as an endothermic reaction and photosynthesis as an endothermic reaction, why?
During respiration, glucose combines with oxygen to form carbon dioxide and water. Energy is produced in this process, so respiration is an exothermic reaction.
In photosynthesis, green plants absorb the energy of sunlight and make food. Since energy is absorbed in this process, photosynthesis is an endothermic reaction.
19. What is the difference between displacement and double displacement reactions? Write the equations for these reactions.
Displacement Reaction :-
The reactions in which one element replaces another element in the compound are called displacement reactions. Generally more reactive element displaces less reactive element from its compound. For example, when an iron nail is dipped in a solution of copper sulphate, iron displaces copper from copper sulphate and a blue-brown layer of copper is deposited on the iron nail.
Fe + CuSO4 → FeSO4 + Cu
Double displacement reaction:
The reactions in which two compounds react by exchange of ions to form two new compounds are called double displacement reactions.
like :-
AgNO3 + NaCl → AgCl + NaNO3
(white precipitate)
20. Explain oxidation and reduction reactions with the help of chemical equations.
Anodization:-
They are reactions in which oxygen is added to the reactant substance. for example-
2Cu + O2 → 2CuO (oxidation of copper to copper oxide)
Reduction :-
They are reactions in which oxygen is lost from the reactant substance.
like :-
CuO + H2 → Cu + H2O (reduction of copper oxide to copper)
21. Why are oily and fatty foods affected by nitrogen?
When food is kept for a long period of time, air oxidisation of the fats and oils present in them gives rise to unpleasant odor and unpleasant taste in the food items. This is called perniciousness. To prevent this oxidization of foods containing fats and oils, such foods are packed in nitrogen gas. Nitrogen gas, being an inert gas, prevents the oxidation of fats and oils in food.
22. Write balanced chemical equations for the following reactions and also state the types of reactions:-
1. Nitrogen combines with hydrogen gas to form ammonia.
2. On heating lead nitrate, lead oxide, nitrogen dioxide and oxygen are formed.
3. Barium chloride reacts with aluminum sulphate to give a precipitate of aluminum chloride and barium sulphate.
4. Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
1. N2 + 3H2 → 2NH3 (Combination reaction).
2. 2Pb(NO3)2 → 2PbO + 4NO2 + O2 (thermal decomposition or thermal decomposition reaction).
3. 3BaCl2 + Al2(SO4)3 → 3BaSO4 + 2AlCl3 (Diffusion reaction).
4. 2K + 2H2O → 2KOH + H2 (displacement reaction).
23. What is a decomposition reaction called?
Decomposition reactions:-
The reactions in which a compound breaks down into two or more simpler substances are called decomposition reactions.
Each decomposition reaction releases heat.
24. How will you separate copper from copper sulphate solution? Explain with reaction?
The solution of copper sulphate is treated with a metal whose reactivity is more than that of copper, such as :-
The chemical equation for Zn, Fe, Pb will be as follows:
Zn + CuSO4 --> ZnSO4 + Cu
In this reaction, Zn reacts with a solution of copper sulphate to form zinc sulphate and copper is obtained. This is an example of a displacement reaction.
25. What is a precipitation reaction? Write the equation.
The chemical reaction in which a substance insoluble in water is formed and solidified as a precipitate is called a precipitation reaction.
like :-
NA2SO4 + BaCl2 --> BaSO4 + 2NaCl In this chemical reaction, BaSO4 is being formed as a precipitate.
26. In the refining of silver, copper metal is displaced from silver nitrate solution to obtain silver, write the chemical reaction for this process?
Cu + AgNo3 --> CuNo3 + Ag
27. Why do we paint iron objects?
When iron objects come in contact with acid, moisture, etc., they start corrosion or get destroyed, they are painted to protect them from destruction. It protects against exposure to moisture, so iron objects are painted.
Other important questions:-
1. On what basis is the equilibrium of a chemical equation done?
Based on the law of conservation of mass.
2. Which gas do the chips makers put in the bag of chips so that they cannot be oxidised?
nitrogen gas.
3. What is the role of a catalyst in a chemical reaction?
Catalysts can speed up or slow down any chemical reaction but themselves remain unchanged.
4. What is a chemical reaction called?
The conversion of one or more substances into another substance, which has different composition and properties, is called a chemical reaction.
5. Which gas is released when potassium chlorate is heated?
Oxygen gas is evolved when potassium chlorant is heated.
6. What is the change in heat to heat when calcium oxide is dissolved in water?
Heat is released when calcium oxide (CaO) is dissolved in water.
7. Which gas is released when a reactive metal is reacted with dilute sulfuric acid?
Hydrogen gas is released.
8. What is the reaction which is used in black and white photography?
2AgBr –(Sunlight) 2Ag(s) +Br2(g)
9. What type of reaction is the combustion of coal?
Combination reaction and oxidation.
10. What is a redox reaction called?
The reaction in which one reactant is oxidised and the other reactant is reduced is called redox (oxidation-reduction) reaction.
11. Write an example of redox reaction.
ZnO + C = Zn + CO
12. What happens when a magnesium ribbon is burnt in air?
White magnesium oxide.
13. When magnesium ribbon is burnt in air, is magnesium oxidised (oxidised) or reduced?
Magnesium is anabolic.
14. What will happen on heating green colored ferrous sulphate crystals?
Ferrous sulphate crystals turn white on burning.
15. Name three metals more reactive than copper.
Iron (Fe), Zinc (Zn) and Magnesium (Mg)
16. What is the chemical formula of marble?
CaCO3 (Calcium Carbonate)
17. Write the order of reactivity of Zn, Pb and Cu.
Zn>Pb>Cu
18. On the basis of which observations the occurrence of a chemical reaction is known?
The occurrence of a chemical reaction is known by the following observations. Having these observations, we can say that the given reaction is a chemical reaction-
1. Change in physical state of matter
2. Change the color of the substance
3. release of a gas
4. Change in the temperature of the reaction.
19. What are chemical equations called? explain.
A chemical equation is the representation of all the reactants and products present in a chemical reaction and their physical state in the form of symbols. The description of a chemical reaction in the form of a sentence becomes very long, so it can be written in a short form. Its simplest method is word equation. For example, when magnesium reacts with oxygen, magnesium oxide is formed. Its word equation will be as follows - Magnesium (reactant) + Oxygen = Magnesium oxide (product)
In this reaction, magnesium and oxygen are substances in which chemical changes take place, they are called reactants. A new substance magnesium oxide is formed from this reaction, this is called a product.
20. How is a chemical equation written? Explain with example.
Chemical equations can be written in two ways-
1. Word Equation- In this equation, the formation of products from reactants is shown by marking an arrow. Write the reactants on the left and the products on the right and put a sign of addition (+) between all the reactants and products. The arrowhead points towards the product. This gives the direction of the reaction to take place.
For example, magnesium (reactant) + oxygen = magnesium oxide (product)
2. Equation in the form of a formula- Chemical equation is written in a concise form by using chemical formula in place of words, which makes it more useful.
A chemical equation represents a chemical reaction.
E.g. 2Mg + O2 = 2MgO
21. What is Oxidation? Explain with example.
That chemical reaction, in which oxygen or electronegative part of a substance is increased or hydrogen or electronegative part is decreased, is called oxidation. Example- (1) Mg + O2 = MgO2, Example (2) H2S + Cl2 = 2HCl + S In example (1), the electronegative part of O2 in Mg has increased while in example (2), H2 means electronegative part in S. Wealth part has decreased.
22. What will be the balanced equation of CH4(g) + O2 = CO2 (g) + H2O?
CH4(g) + 2O2(g) = CO2 (g) + 2H2O(l)
23. Write the balanced equation of the reaction of N2 and H2.
N2(g) + 3H2(g) = 2NH3(g)
24. Write balanced chemical equation for the following reaction: Sodium sulphite + water + chlorine = sodium sulphate + hydrochloric acid
Na2SO3(aq) + H2O + Cl2(g) = Na2SO4(aq) + 2HCl(g)
25. What are redox reactions? Identify the oxidised and reduced substances in the following reaction - ZnO + C = Zn + CO
Redox Reaction- Such chemical reactions, in which one reactant is oxidised and the other reactant is reduced, that is, in which oxidation and reduction reactions take place simultaneously, they are called redox reactions. In the reaction given in the question, reduction of Zn and oxidation of C takes place.
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