Chemical Reactions and Equations Class 10 Science Exam Questions

Exam Questions Class 10

Please refer to Chemical Reactions And Equations Class 10 Science Exam Questions provided below. These questions and answers for Class 10 Science have been designed based on the past trend of questions and important topics in your class 10 Science books. You should go through all Class 10 Science Important Questions provided by our teachers which will help you to get more marks in upcoming exams.

Class 10 Science Exam Questions Chemical Reactions And Equations

Class 10 Science students should read and understand the important questions and answers provided below for Chemical Reactions And Equations which will help them to understand all important and difficult topics.

Question: Write a balanced chemical equation for the reaction between sodium carbonate and hydrochloric acid indicating the physical state of the reactants and the products.


Question: Balance the following chemical equation :
Pb(NO3)2(s) heat→ PbO(s) + NO2(g) + O2(g) 


Question: Balance the following chemical equation :
FeSO4 heat→ Fe2O3 + SO2 + SO3 


Question: Balance the following chemical equation :
 Fe(s) + H2O(g) Fe3O4(s) + H2(g)


Question: Balance the following chemical reaction :
MnO2 + HCl→ MnCl2 + Cl2 + H2O


Question: What change in colour is observed when white silver chloride is left exposed to sunlight? What type of chemical reaction is this?  


When white silver chloride is left exposed to sunlight, its colour changes to grey due to the formation of silver.

This type of reaction is called photodecomposition reaction.

Question. What is a redox reaction? When a magnesium ribbon burns in air with a dazzling name and forms a white ash, is magnesium oxidised or reduced? Why? 


A reaction in which oxidation and reduction take place simultaneously is called redox reaction.
On heating in oxygen/air, magnesium burns with a dazzling white light to give magnesium oxide.
2Mg + O2 heat→ 2MgO
Here, magnesium is oxidised as addition of oxygen has taken place

Question: What happens chemically when quick lime is added to water?


Quick lime reacts vigorously with water to produce calcium hydroxide (slaked lime) releasing a large amount of heat (exothermic reaction).

Question: (a) What is the colour of ferrous sulphate crystals? How does this colour change afer heating?
(b) Name the products formed on strongly heating ferrous sulphate crystals. What type of chemical reaction occurs in this change? 


(a) Ferrous sulphate crystals (FeSO4.7H2O) are light green in colour.
When it is heated, white colour solid is formed.

(b) When anhydrous ferrous sulphate is further heated strongly, it decomposes to give ferrous oxide (Fe2O3) and oxides of sulphur.

this type of chemical reaction is known as decomposition reaction.

Question: What happens when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride? State the physical conditions of reactants in which the reaction between them will not take place. Write the balanced chemical equation for the reaction and name the type of reaction.


When an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride then, white precipitate of barium sulphate (BaSO4) is formed.
Na2SO4(aq) + BaCl2(aq) →BaSO4(s) + 2NaCl(aq)
If the reactants are present in solid state then no reaction will take place between them. This type of reaction is called double displacement reaction or precipitation reaction.

Question: In electrolysis of water, why is the volume of gas collected over one electrode double than that of gas collected over the other electrode?


In electrolysis of water, hydrogen (H2) gas is liberated at cathode while oxygen (O2) gas is liberated at anode. e overall reaction is 
2H2O(l) Electric current→2H2(g) + O2(g)
From the above reaction, it is clear that amount of
H2 liberated is twice that of O2.

Question: (i) What is observed when a solution of potassium iodide is added to a solution of lead nitrate taken in a test tube?
(ii) What type of reaction is this?
(iii) Write a balanced chemical equation to represent the above reaction.


(i) When lead nitrate is added to potassium iodide then yellow precipitate of lead iodide is formed along with potassium nitrate.
(ii) This type of reaction is called precipitation reaction in which one of the products formed is an insoluble substance.
(iii) Chemical reaction will be as follows :

Question: Give an example of decomposition reaction. Describe an activity to illustrate such a reaction by heating.


Those reactions in which a compound breaks down into two or more simpler substances are known as decomposition reactions.
Aim : To show thermal decomposition reaction of ferrous sulphate.
Material required : Ferrous sulphate crystals, dry test tube, burner

 Procedure : 1. Take 2 g of ferrous sulphate crystals
in a dry test tube.
2. Observe the colour of ferrous sulphate crystals.
3.Heat the crystals of ferrous sulphate over the Name of a burner for some time.
4.Observe the crystals afer heating for 5 minutes

Observation :The pale green colour of ferrous sulphate crystals changes to reddish brown ferric oxide and smell of burning sulphur is observed.

Question: What is an oxidation reaction? Identify in the following reaction :
ZnO + C → Zn + CO
(i) the substance oxidised and
(ii) the substance reduced. 


The reaction in which oxygen is added or hydrogen is removed or loss of electrons takes place is called an oxidation reaction. In the reaction,

(i) Carbon is getting oxidised to carbon monoxide.
(ii) Zinc oxide is getting reduced to zinc.

Very Short Answers Type Questions

Question: What is a chemical reaction ?
Answer : A process in which a new substance is formed and original substance lose its identity is called a chemical change.

Question:. Why is a copper vessel covered with a green coating in rainy season ?
Answer : Copper vessel is covered with a green coating in rainy season due to the attack of oxygen, carbon dioxide and water vapours of the air on copper forming green coloured basic copper carbonate.

Question: When the powder of common metal is heated in open china dish, its colour turns black. However, when hydrogen is passed over the hot black substance so formed, it regains its original colour. Based on the above information answer the following questions :
(a) What type of chemical reaction takes place in each of the two given steps ?
(b) Name the metal initially taken in the powder form.
Answer : (a) In the first step, oxidation takes place and in the second step, redox reaction takes place.
(b) The metal initially taken in powder form was copper.

Question: Identify the type of reaction :
Zn + CuSO4 → ZnSO4 + Cu
Answer : Displacement reaction.

Question: What is the reason behind various metals such as iron get wasted every year in our country ?
Answer : Due to corrosion various metals such as iron get wasted every year in our country.

Question: Which substance is used in white washing ?
Answer : Calcium hydroxide (slaked lime) is used in white washing.

Question: Name the most reactive metal and least reactive metal of the activity series of metals.
Answer : Most reactive metal is potassium and least reactive metal is gold.

Question: Why is hydrogen included in activity series of metals ?
Answer : Hydrogen is included in activity series of metals because like metals, hydrogen can also lose electrons to form positive ions.

Question: A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water it forms a solution which turns red litmus blue. Identify X and also write the chemical reactions involved.
Answer : Calcium oxide
CaO(s) + H2O(l) → Ca(OH)2(aq)

Question: What happens when a dilute solution of ferrous sulphate was gradually added to a beaker containing acidified permanganate solution ? Explain the reason. 
Answer : The light purple colour of the solution fades and finally disappears. The colour of the solution disappears because of dilution. No reaction is involved in this.

Question: Why should an equation be balanced ?
Answer : An equation should be balanced because according to the law of conservation of mass, mass can neither be created nor be destroyed. Therefore, the number of atoms on both the sides of equation must be equal.

Short Answers Type Questions

Question: Mention with reason the colour changes observed when :
(a) silver chloride is exposed to sunlight.
(b) copper powder is strongly heated in the presence of oxygen.
(c) a piece of zinc is dropped in copper sulphate solution.
Answer :
(a) When silver chloride (white) is exposed to sunlight, it undergoes photochemical decomposition forming black metallic coloured silver and greenish yellow gas chlorine. Thus, the change in colour is observed due to the oxidation of silver chloride in the presence of sunlight.
(b) Heated copper metal reacts with oxygen to form the black copper oxide. Thus, the change in colour is observed when copper powder is strongly heated.
2Cu (s) + O2(g) → 2CuO (s)
(c) On adding zinc to CuSO4 solution, zinc displaces copper from copper sulphate and forms zinc sulphate solution. This is indicated by colour change from blue to colourless. CuSO4 solution has a blue colour while ZnSO4 solution is colourless.
Zn(s) + CuSO4(aq) → Cu(s) + ZnSO4(aq)

Question: 2 g of silver chloride is taken in a china dish and the china dish is placed in sunlight for sometime. What will be your observation in this case ? Write the chemical reaction involved in the form of a balanced chemical equation. Identify the type of chemical reaction.
Answer :

Chemical Reactions and Equations Class 10 Science Exam Questions

Initially the colour of silver chloride is white but when it is kept in sunlight it breaks down to give silver and chlorine. Hence, the colour changes to grey. It is an example of photo-chemical decomposition.

Question: Identify the type of reactions taking place in each of the following cases and write the balanced chemical equation for the reactions.
(a) Zinc reacts with silver nitrate to produce zinc nitrate and silver.
(b) Potassium iodide reacts with lead nitrate to produce potassium nitrate and lead iodide.
Answer : (a) The given reaction is a displacement reaction.
Zn(s) + 2 AgNO3(aq) → Zn(NO3)2 (aq) + 2Ag(s)
(b) It is a double displacement reaction.
2KI(aq) + Pb(NO3)2(aq) → 2 KNO3(aq) + PbI2(s)

Question: What does one mean by exothermic and endothermic reactions ? Give examples.
Answer : Chemical reactions that release energy in the form of heat, light or sound are called exothermic reactions. Combination reactions are exothermic.
Example : Sodium oxide dissolves in water to form sodium hydroxide and releases large amount of energy.
Na2O + H2O → 2NaOH + Energy
Reactions that absorb energy or require energy in order to proceed are called endothermic reactions. 
Example : Combination of nitrogen and oxygen to form nitric oxide.
N2 + O2 + Heat → 2NO

Question: What do you mean by a precipitation reaction ?
Explain by giving examples.
Answer : A reaction in which an insoluble solid (called precipitate) is formed is called a precipitation reaction.
For example :

Chemical Reactions and Equations Class 10 Science Exam Questions

In this reaction, calcium carbonate is obtained as a precipitate. Hence, it is a precipitation reaction.

Question: Identify the oxidising agent (oxidant) in the following reactions :
(a) Pb3O4 + 8HCl → 3PbCl2 + Cl2 + 4H2O
(b) 2Mg + O2 → 2MgO
(c) CuSO4 + Zn → Cu + ZnSO4
(d) V2O5 + 5Ca → 2V + 5CaO
(e) 3Fe + 4H2O → Fe3O4 + 4H2
(f) CuO + H2 → Cu + H2O
Answer : (a) Pb3O4 (b) O2
(c) CuSO4 (d) V2O5
(e) H2O (f) CuO

Question: Why should a magnesium ribbon be cleaned before burning in air ?
Answer : Magnesium is a very reactive metal, it reacts with oxygen to form a layer of magnesium oxide on its surface when stored. This layer of magnesium oxide is quite stable and prevents further reaction of magnesium with oxygen. Hence, this layer is removed by cleaning magnesium ribbon by sand paper so that the underlying metal can be exposed into air.

Question: A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining.
(a) Why do silver articles turn black when kept in the open for a few days ? Name the phenomenon involved.
(b) Name the black substance formed and give its chemical formula.
Answer : (a) Metals such as silver when attacked by substances around it such as moisture, acids, gases etc., are said to corrode and this phenomenon is called corrosion.
(b) The black substance is formed because silver (Ag) reacts with H2S present in air. It forms thin black coating of silver sulphide (Ag2S).

Question: Oil and fat containing food items are flushed with nitrogen. Why ?
Explain why, food products containing fats and oils (like potato chips) are packaged in nitrogen.
Answer : Oil and fat containing food items are flushed with nitrogen because it is an inert gas and does not easily react with these substances. On the other hand, oxygen reacts with food substances and makes them rancid.
Thus, bags used in packing food items are flushed with nitrogen gas to remove oxygen inside the pack. When oxygen is not present inside the pack, rancidity of oil and fat containing food items is avoided.

Question: Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773 K to form ammonia gas.
(b) Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.
(c) Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H2SO4.
(d) Ethene is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light.
Answer : (a) N2(g) + 3H2 → 2NH3(g)
Combination Reaction
(b) NaOH(aq) + CH3COOH(aq) → CH3COONa(aq) + H2O(l)
Double displacement reaction or neutralisation reaction.
(c) C2H5OH(l) + CH3COOH(l) → CH3COOC2H5(l) + H2O(l)
Double displacement reaction or Esterificaton reaction.
(d) C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(g) + Heat + Light
Redox reaction or combustion reaction.

Question: Write the balanced chemical equations for the following reactions and identify the type of reaction in each case :
(a) Thermite reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
(b) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.
(c) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
(d) Ethanol is burnt in air to form carbon dioxide, water and releases heat.
Answer : (a) Fe2O3(s) + 2Al(s) → Al2O3(s) + 2Fe(l) + Heat 
Displacement reaction or redox reaction
(b) 3Mg(s) + N2(g) → Mg3N2(s)
Combination reaction
(c) 2KI(aq) + Cl2(g) → 2KCl(aq) + I2(s)
Displacement reaction

Question: In the reaction :
MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
(a) Name the compound (i) oxidised, (ii) reduced.
(b) Define oxidation and reduction on its basis.
Answer : (a) (i) HCl is oxidised in the reaction.
(ii) MnO2 is reduced in the reaction.
(b) Oxidation is the gain of oxygen or loss of hydrogen whereas reduction is the gain of hydrogen or loss of oxygen.

Long Answers Type Questions

Question: Write balanced chemical equations to explain what happens, when
(i) Mercuric oxide is heated.
(ii) Mixture of cuprous oxide and cuprous sulphide is heated.
(iii) Aluminium is reacted with manganese dioxide.
(iv) Ferric oxide is reduced with aluminium.
(v) Zinc carbonate undergoes calcination.
Answer : (i) Cinnabar (HgS) is an ore of mercury. When it is heated in air, it is first converted into mercuric oxide (HgO). Mercuric oxide is then reduced to mercury on further heating.

Chemical Reactions and Equations Class 10 Science Exam Questions

(ii) When a mixture of copper oxide and copper sulphide is heated metallic copper is formed along with the evolution of the sulphur dioxide gas. The reaction equation is as follows:
2Cu2O + Cu2S → 6Cu + SO2
(iii) When aluminium powder is reacted with manganese dioxide, Manganese and aluminium oxide are formed with the evolution of heat and the following reaction takes place :
3MnO2(s) + 4Al(s) → 3Mn(l) + 2Al2O3(s) + Heat
(iv) When ferric oxide is reduced with aluminium a displacement reaction takes place and this reaction is highly exothermic. The amount of heat evolved is so large that the metals are produced in the molten state. In fact, the reaction of iron (III) oxide (Fe2O3) with aluminium is used to join railway tracks or cracked machine parts. This reaction is known as the thermite reaction.
Fe2O3(s) + 2Al(s) → 2Fe(l) + Al2O3(s) + Heat 
(v) The carbonate ores are changed into oxides by heating strongly in limited air. This process isknown as calcination. The chemical reaction that  takes place during calcination of zinc ores can be shown as follows :

Chemical Reactions and Equations Class 10 Science Exam Questions

Question: (a) State the various characteristics of chemical reactions.
(b) State one characteristic each of the chemical reaction which takes place when :
(i) Dilute hydrochloric acid is added to sodium carbonate.
(ii) Lemon juice is added gradually to potassium permanganate solution.
(iii) Dilute sulphuric acid is added to barium chloride solution.
(iv) Quick lime is treated with water.
(v) Wax is burned in the form of a candle.
Answer : (a) The various characteristics of chemical reactions are :
(i) Evolution of a gas
(ii) Formation of a precipitate
(iii) Change in colour
(iv) Change in temperature
(v) Change in state.
(b) (i) Evolution of carbon dioxide gas.
(ii) Change in colour from purple to colourless.
(iii) Formation of white precipitate of barium sulphate.
(iv) Change in temperature.
(v) Change in state from solid to liquid and gas.

Question: Give the characteristic tests for the following gases :
(a) CO2, (b) SO2, (c) O2, (d) H2.
Answer : The characteristic test for
(a) Carbon dioxide (CO2) : This gas turns lime water milky when passed through it due to the formation of insoluble calcium carbonate.
Ca(OH)2 + CO2 → CaCO3 + H2O
Lime water Carbon dioxide Calcium carbonate
(b) Sulphur dioxide (SO2) : This gas when passed through acidic potassium permanganate solution (purple in colour) turns it colourless because SO2 is a strong reducing agent.
2KMnO4 + 2H2O + 5SO2 → K2SO4 + 2MnSO4 Manganese sulphate + 2H2SO4
(c) Oxygen : The evolution of oxygen (O2) gas during a reaction can be confirmed by bringing a burning candle near the mouth of the test tube containing the reaction mixture. The intensity of the flame increases because oxygen supports burning.

Chemical Reactions and Equations Class 10 Science Exam Questions

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