CBSE Class 10 Science Chapter-1 Chemical Reactions and Equations Important Questions – Free PDF Download
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CBSE Class 10 Science Chapter-1 Important Questions
CBSE Class 10 science Important Questions Chapter 1 – Chemical Reactions and Equations
5 Mark Questions
1. You are given with
(a) Iron Nails
(b) CuSO4 solution
(c) Bacl2
(d) Cu powder
(e) Ferrous sulphate crystal
(f) Quick lime.
Make five reactions that can take place from these materials.
Ans. (i) 
(ii) 
(iii) 
(iv) 
(v) 
2. A metal is heated with dil H2SO4. The gas evolved is collected by the method shown in the figure: Answer the following
(a) Name the gas.
(b) Name the method of collection of gas.
(c) Is the gas soluble or insoluble in water?
(d) Is the gas lighter or heavier than air?
Ans. (a) H2 gas
(b) Gas is collected over water by a method called downward displacement method.
(c) Since collected over water so it is insoluble.
(d) The gas is lighter than air.
3. With the help of an activity show that iron is more reactive than copper?
Ans. First take some aqueous solution of Cuso4 (blue is colour) and dip iron nails into it leave for half an hour the blue colour of the solution changes into light green. At the same time brown deposit appears on the nails. This happens because iron is placed above copper in reactivity series hence it displaces copper from cuso4 solution. The brown deposit is of copper.
i.e. 
4. Observe the following activity & answer the questions
a. Do you observe anything happening around the zinc granules?
b. Is there any change in its temperature?
c. Why is glass tube not dipped in dil 
?
d. How is 
gas collected by downward displacement or upward displacement of water?
e. Is gas soluble or insoluble in water?
f. Is gas heavier or lighter than air?
Ans. a. Bubbles of hydrogen gas.
b. Yes temperature will increase.
c. will rise in glass tube, preventing to evolve
d. downward displacement
e. Insoluble
f. lighter than air
5. A reddish brown metal X when heated in presence of oxygen forms a black compound Y Which is basic in nature when heated with hydrogen gas gives back X.
Identify X & Y. Write the chemical reaction between Y & Identify the substance being oxidized & Reduced.
Ans. Oxygen reacts with copper to form copper oxides which has black colour
The copper (II) ovide is losing oxygen and is being reduced. The hydrogen is gaining
6. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Ans. When iron nail is dipped in copper sulphate solution, than iron sulphate solution and copper solution and copper metal are formed:
CuSO4 (aq) + Fe (s) 
FeSO4 (aq) + Cu (s)
In this reaction, iron displaces copper from copper sulphate solution. The deep blue colour of copper sulphate fades due to the formation of light green solution of iron sulphate.
7. Identify the substances that are oxidized and the substances that are reduced in the following reactions.
(i) 4Na (s) + O2 (g) 2Na2O (s)
(ii) CuO (s) + H2 Cu (s) + H2O (l)
Ans. (i) 4Na + O2 2Na2O
In this reaction, Na is oxidized because it combines with O2 to form Na2O. O2 is reduced because it is converted into Na2O.
(ii) CuO + H2 Cu + H2O
In this reaction, CuO is reduced because it loses oxygen. H2 is oxidized because it combines with oxygen of CuO to form water
8. Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and Sulpher dioxide.
(c) Barium chloride reacts with aluminum sulphate to give aluminum chloride and precipitate of barium sulphate
Ans. (a) H2 +N2 NH3
3H2 +N2 2NH3
(b) H2S + O2 H2O + SO2
2H2S + 3O2 2H2O + 2SO2
(c) BaCl2 + Al2(SO4)3 AlCl3 +BaSO4
3BaCl2 + Al2(SO4)3 2AlCl3 +3BaSO4
(d) K + H2O KOH + H2
2K + 2H2O 2KOH + H2
9. Balance the following chemical equations:
(a) HNO3 + Ca(OH)2 Ca(OH)2 àCa(NO3)2 +H2O
(b) NaOH +H2SO4 Na2SO4 +H2O
(c) NaCl +AgNO3 AgCl + NaNO3
(d) BaCl2 +H2SO4 BaSO4 +HCl
Ans. Balanced chemical equation are
(a) 2HNO3 + Ca(OH)2 Ca(OH)2 àCa(NO3)2 +2H2O
(b) 2NaOH +H2SO4 Na2SO4 +2H2O
(c) NaCl +AgNO3 AgCl + NaNO3
(d) BaCl2 +H2SO4 BaSO4 +2HCl
10. Write the balanced chemical equations for the following reactions.
(a) Calcium hydroxide + Carbon dioxide Calcium carbonate + Water
(b) Zinc + Silver nitrate Zinc nitrate + Silver
(c) Aluminum + Copper chloride Aluminum chloride +Copper
(d) Barium chloride + Potassium sulphate Barium sulphate + potassium chloride
Ans. Balanced chemical equation for reactions are
(a) Ca(OH)2 + CO2 CaCO3 + H2O
(b) Zn + 2AgNO3 Zn(NO3)2 +2Ag
(c) 2Al + 3Cl2 2AlCl3 + 3Cu
(d) BaCl2 + K2SO4 BaSO4 + 2KCl
11. Write the balanced chemical equation for the following and identify the type of reaction in each case.
(a) Potassium bromide (s) + Barium iodide (aq) Potassium iodide (aq) + Barium bromide(s)
(b) Zinc carbonate (s) Zinc oxide (s) + Carbon dioxide (g)
(c) Hydrogen (g) + Chlorine (g) Hydrogen chloride (g)
(d) Magnesium (s) + Hydrochloric acid (aq) Magnesium chloride (aq) + Hydrogen (g)
Ans. Balanced equations are
(a) 2KBr (aq) + BaI2 ( aq) 2KI (aq) + Br2 (displacement reaction)
(b) ZnO3 (s) ZnO (s) + CO2 (g) (decomposition reaction)
(c) H2 (g) + Cl2 (g) 2HCl (combination reaction)
(d) Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g) (displacement reaction)
12. What does one mean by exothermic and endothermic reactions? Give examples.
Ans. A reaction in which energy is released in the form of heat or light is called exothermic reaction. Example of exothermic reaction are:
CH4 + 2O2 CO2 + 2H2O + heat
2Al + FeO3 Al2O3 + Fe + heat
A reaction in which energy is absorbed from the surrounding and cooling is produced is called endothermic reaction. Example of exothermic reaction are:
a. CaCO3 CaO + CO2
b. N2 + O2 2NO
13. Why decomposition reactions are called the opposite of combination reactions? Write equations for these reactions.
Ans. NH4Cl (s) HCl (g) + NH3 (g)
In a decomposition reaction, a single substance breaks down into two or more substance while in a combination reaction, two or more substances react to produce one substance. Therefore, decomposition reactions are called opposite of combination reactions.
Example of decomposition reaction: Example of combination reaction:
CaO (s) + CO2 (g) CaCO3 (s)
14. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Ans. Decomposition by heat:
CaCO3(S) + heat CaO (s) + CO2 (g)
Decomposition by electricity:
2H2O + light 2H2 (g) + O2 (g)
Decomposition by light:
2AgBr (s) + light 2Ag (s) + Br2
15. What is difference between displacement and double displacement reactions? Write equations for these reactions.
Ans. In displacement reaction, more reactive element displaces the less reactive element from its compound. For example
Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s)
But in double displacement reaction, exchange of ions takes place. For example
HCl (aq) + AgNO3 (aq) AgCl (s) + HNO3 (aq)
16. Explain the following in terms of gain and loss of oxygen with two examples each?
a. Oxidation
b. Reduction
Ans. Oxidation- addition of oxygen or removal of hydrogen in a chemical reaction is called oxidation reaction. For example
2Cu +O2 2CuO
4Al + 3O2 2Al2O3
Reduction- addition of hydrogen or removal of oxygen in a chemical reaction is called oxidation reaction. For example
CuO +H2 Cu +H2O
H2S + Cl2 2HCl +S
17. Explain the following terms with one example each.
a. Corrosion
b. Rancidity.
Ans. Corrosion- action of air, water, acid or other substance on metal surface to form oxides and carbonates is called corrosion. Corrosion of iron is called rusting. Green coating on copper and black coating on silver is examples of corrosion.
Rancidity-change in smell of food item containing fat and oil when kept open for longer time due to oxidation is called rancidity. To prevent rancidity food items are flushed with nitrogen or kept in airtight containers.