Class 10 Science · Chapter 1

Chemical Reactions and Equations

298 Class 10 Science questions on Chemical Reactions and Equations from the NCERT textbook, NCERT Exemplar and CBSE board papers 2018–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 10 of 15

1. Q181 CBSE 2024
   The ​products ​obtained when ​Lead ​nitrate is heated in ​a ​boiling ​tube.

   1. (a)$\text{PbO}$, ${\text{N}}_2\text{O}$ and ${\text{O}}_2$
   2. (b)$\text{NO}$, $\text{PbO}$ and ${\text{O}}_2$
   3. (c)$\text{Pb}({\text{NO}}_2{)}_2$ and ${\text{O}}_2$
   4. (d)${\text{NO}}_2$, $\text{PbO}$ and ${\text{O}}_2$
   Show answer

   (d) ${\text{NO}}_2$, $\text{PbO}$ and ${\text{O}}_2$

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2. Q182 CBSE 2024
   When aqueous solutions ​of ​barium ​chloride and sodium sulphate react ​together, an ​insoluble substance along with aqueous solution of sodium chloride is formed. This reaction ​is an example ​of a :

   1. (a)combination reaction
   2. (b)decomposition reaction
   3. (c)displacement reaction
   4. (d)double displacement reaction
   Show answer

   (d) double displacement reaction

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3. Q183 CBSE 2024
   Identify ​the ​correct ​statement ​about the ​following reaction : $2{\text{H}}_2\text{S}+{\text{SO}}_2⟶2{\text{H}}_2\text{O}+\text{S}$

   1. (a)${\text{H}}_2\text{S}$ is oxidising agent and ${\text{SO}}_2$ is reducing agent.
   2. (b)${\text{H}}_2\text{S}$ is reduced to sulphur.
   3. (c)${\text{SO}}_2$ is oxidising agent and ${\text{H}}_2\text{S}$ is reducing agent.
   4. (d)${\text{SO}}_2$ is oxidised to sulphur.
   Show answer

   (c) ${\text{SO}}_2$ is oxidising agent and ${\text{H}}_2\text{S}$ is reducing agent.

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4. Q184 CBSE 2024
   Consider ​the ​following chemical ​equations : $p{\text{MnO}}_2+q\text{Al}\to r\text{Mn}+s{\text{Al}}_2{\text{O}}_3$ To ​balance this chemical equation the ​values of the coefficients $p$, $q$, $r$ and $s$ must be respectively :

   1. (a)3, 2, 3, 4
   2. (b)4, 3, 4, 2
   3. (c)3, 4, 3, 2
   4. (d)4, 2, 4, 3
   Show answer

   (c) 3, 4, 3, 2

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5. Q185 CBSE 2024
   ${\text{MnO}}_2+4\text{HCl}\to {\text{MnCl}}_2+2{\text{H}}_2\text{O}+{\text{Cl}}_2$ The ​reaction given above ​is a redox ​reaction ​because in this case :

   1. (a)${\text{MnO}}_2$ is oxidised and $\text{HCl}$ is reduced.
   2. (b)$\text{HCl}$ is oxidised.
   3. (c)${\text{MnO}}_2$ is reduced.
   4. (d)${\text{MnO}}_2$ is reduced and $\text{HCl}$ is oxidised.
   Show answer

   (d) ${\text{MnO}}_2$ is reduced and $\text{HCl}$ is oxidised.

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6. Q186 CBSE 2024
   Which ​one of ​the following reactions ​is ​different ​from the remaining ​three ?

   1. (a)$\text{NaCl}+{\text{AgNO}}_3\to \text{AgCl}+{\text{NaNO}}_3$
   2. (b)$\text{CaO}+{\text{H}}_2\text{O}\to {\text{Ca(OH)}}_2$
   3. (c)${\text{KNO}}_3+{\text{H}}_2{\text{SO}}_4\to {\text{KHSO}}_4+{\text{HNO}}_3$
   4. (d)${\text{ZnCl}}_2+{\text{H}}_2\text{S}\to \text{ZnS}+2\text{HCl}$
   Show answer

   (b) $\text{CaO}+{\text{H}}_2\text{O}\to {\text{Ca(OH)}}_2$

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7. Q187 CBSE 2024
   Which one ​of the following ​is ​an example of ​endothermic ​process ​?

   1. (a)Digestion of food in human body
   2. (b)Formation of slaked lime
   3. (c)Decomposition of vegetable matter into compost
   4. (d)Decomposition of silver bromide into silver and bromine
   Show answer

   (d) Decomposition of silver bromide into silver and bromine

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8. Q188 CBSE 2024
   Select the ​correct ​statement ​from the ​following about ​the reaction : $\text{CuO}+{\text{H}}_2⟶\text{Cu}+{\text{H}}_2\text{O}$

   1. (a)$\text{CuO}$ is getting oxidised and ${\text{H}}_2$ is getting reduced.
   2. (b)${\text{H}}_2$ is getting oxidised and $\text{CuO}$ is getting reduced.
   3. (c)$\text{CuO}$ is a reducing agent.
   4. (d)${\text{H}}_2$ is an oxidising agent.
   Show answer

   (b) ${\text{H}}_2$ is getting oxidised and $\text{CuO}$ is getting reduced.

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9. Q189 CBSE 2024
   Name the type of chemical ​reaction in ​which calcium oxide reacts ​with water. Justify your ​answer by giving balanced chemical ​equation for ​the chemical reaction.
   Show answer

   Calcium oxide and water combine to form a single product, calcium hydroxide, so it is a combination reaction.

   It is a combination reaction (it is also exothermic). Justification: calcium oxide and water combine to form a single product, calcium hydroxide (slaked lime), and heat is released: $\text{CaO}(\text{s})+{\text{H}}_2\text{O}(\text{l})\to {\text{Ca(OH)}}_2(\text{aq})+\text{Heat}$.

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10. Q190 CBSE 2024
    When a ​few ​drops ​of ​Barium chloride solution are added to an aqueous solution of Sodium sulphate, a white precipitate ​is obtained.

    1. (a)Write balanced chemical equation for the ​reaction involved.
    2. (b)​What ​is the other name of this precipitation reaction ? Why is it called so ?
    Show answer

    Barium sulphate precipitates; the reaction is also called double displacement because the two reactants exchange their ions.

    (a) ${\text{Na}}_2{\text{SO}}_4(\text{aq})+{\text{BaCl}}_2(\text{aq})⟶{\text{BaSO}}_4(\text{s})+2\text{NaCl}(\text{aq})$. The white precipitate is barium sulphate. (b) It is a double displacement reaction. It is called so because the two reactants exchange their ions: barium ions combine with sulphate ions to form barium sulphate, and sodium ions combine with chloride ions to form sodium chloride.

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11. Q191 CBSE 2024
    1. (a)​Write the essential conditions for following reaction to ​take place and name its types ​: $$2\text{AgCl}⟶2\text{Ag}+{\text{Cl}}_2$$
    2. (b)Complete the following chemical ​reaction in the ​form of a balanced equation : $${\text{FeSO}}_4\stackrel{\Delta }{\to }{\text{Fe}}_2{\text{O}}_3+\dots \dots +\dots \dots$$
    Show answer

    Silver chloride needs sunlight and undergoes photolytic decomposition; heated ferrous sulphate gives ${\text{Fe}}_2{\text{O}}_3$, ${\text{SO}}_2$ and ${\text{SO}}_3$.

    (a) Essential condition: exposure to sunlight (light energy); white silver chloride turns grey as silver forms, $2\text{AgCl}\stackrel{\text{sunlight}}{\to }2\text{Ag}+{\text{Cl}}_2$. Types: a decomposition reaction, specifically a photolytic (photochemical) decomposition; it absorbs energy, so it is also endothermic. (b) $2{\text{FeSO}}_4\stackrel{\Delta }{\to }{\text{Fe}}_2{\text{O}}_3+{\text{SO}}_2+{\text{SO}}_3$, a thermal decomposition giving ferric oxide, sulphur dioxide and sulphur trioxide.

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12. Q192 CBSE 2024
    When magnesium ribbon ​is burnt ​in air, an ash of white colour ​is produced. ​Write ​chemical equation for the reaction giving the chemical name of the ash produced. ​State the type of ​chemical reaction giving justification for your answer.
    Show answer

    Burning magnesium forms magnesium oxide, $\text{MgO}$, in a combination reaction, since two reactants give a single product.

    Chemical equation: $2\text{Mg}(s)+{\text{O}}_2(g)\to 2\text{MgO}(s)$. The white ash is magnesium oxide ($\text{MgO}$). Type of reaction: combination reaction, because two reactants, magnesium and oxygen, combine to form a single product, magnesium oxide. (The reaction also gives out heat and light, so it is exothermic, and magnesium is oxidised.)

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13. Q193 CBSE 2024
    “No ​precipitation reaction can occur ​without ​exchange of ions between ​the two reactants.” Justify ​this statement giving a balanced chemical ​equation for ​the reaction.
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    A precipitate forms only when the two reactants exchange ions, as ${\text{Ba}}^{2+}$ and ${\text{SO}}_4^{2-}$ combine to give insoluble barium sulphate.

    A precipitate is an insoluble compound formed from the cation of one reactant and the anion of the other, so it can form only when the two reactants exchange their ions — a double displacement reaction. Example: ${\text{Na}}_2{\text{SO}}_4(\text{aq})+{\text{BaCl}}_2(\text{aq})\to {\text{BaSO}}_4(\text{s})\downarrow +2\text{NaCl}(\text{aq})$. Here ${\text{Ba}}^{2+}$ from barium chloride pairs with ${\text{SO}}_4^{2-}$ from sodium sulphate to give the white, insoluble precipitate of barium sulphate, while ${\text{Na}}^{+}$ and ${\text{Cl}}^{-}$ remain in solution as sodium chloride. Without this exchange of ions no barium sulphate could form, and no precipitate would appear.

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14. Q194 CBSE 2024
    Define a ​decomposition reaction. Write an equation ​to show ​thermal ​decomposition of ferrous ​sulphate ​crystals.
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    A decomposition reaction gives two or more simpler products from one reactant; heated ferrous sulphate gives ${\text{Fe}}_2{\text{O}}_3$, ${\text{SO}}_2$ and ${\text{SO}}_3$.

    A decomposition reaction is a reaction in which a single reactant breaks down to give two or more simpler products. Thermal decomposition of ferrous sulphate: $2{\text{FeSO}}_4\text{(s)}\stackrel{\text{heat}}{\to }{\text{Fe}}_2{\text{O}}_3\text{(s)}+{\text{SO}}_2\text{(g)}+{\text{SO}}_3\text{(g)}$, that is, ferrous sulphate gives ferric oxide, sulphur dioxide and sulphur trioxide.

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15. Q195 CBSE 2024
    Give one example of each of the following :

    1. (i)Chemical ​reaction ​showing evolution of gas.
    2. (ii)Change in the colour of the ​substance during ​a chemical ​reaction.
    Show answer

    Zinc with dilute sulphuric acid gives hydrogen gas; an iron nail in copper sulphate solution turns the blue solution pale green.

    (i) Zinc granules with dilute sulphuric acid give off hydrogen gas: $\text{Zn}+{\text{H}}_2{\text{SO}}_4\to {\text{ZnSO}}_4+{\text{H}}_2\uparrow$. (ii) An iron nail in copper sulphate solution turns the blue solution pale green and gets a brown coat of copper: $\text{Fe}+{\text{CuSO}}_4\to {\text{FeSO}}_4+\text{Cu}$. Other correct examples also earn credit.

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16. Q196 CBSE 2024
    Copper powder is taken in a china dish and heated ​over a burner. Name the product formed and state ​its colour. Write the chemical ​equation for ​the ​reaction ​involved.
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    Heated copper powder forms black copper(II) oxide, $\text{CuO}$: $2\text{Cu}+{\text{O}}_2\to 2\text{CuO}$.

    The product is copper(II) oxide, $\text{CuO}$, which is black: the reddish-brown surface of the copper powder becomes coated with it. Equation: $2\text{Cu}+{\text{O}}_2\stackrel{\text{Heat}}{\to }2\text{CuO}$.

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17. Q197 CBSE 2024
    Giving ​one ​example of each, ​differentiate between ​a ​displacement reaction and ​a double ​displacement reaction.
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    In displacement a more reactive element replaces a less reactive one, but in double displacement two compounds exchange ions.

    (1) In a displacement reaction a more reactive element displaces a less reactive element from its compound (element + compound → new compound + new element); in a double displacement reaction two compounds exchange their ions to form two new compounds, and no free element takes part. (2) A displacement reaction takes place only if the displacing element is more reactive than the one it displaces; a double displacement reaction is not decided by the reactivity series and often gives a precipitate. Example of displacement: $\text{Fe}(\text{s})+{\text{CuSO}}_4(\text{aq})\to {\text{FeSO}}_4(\text{aq})+\text{Cu}(\text{s})$. Example of double displacement: ${\text{Na}}_2{\text{SO}}_4(\text{aq})+{\text{BaCl}}_2(\text{aq})\to {\text{BaSO}}_4(\text{s})\downarrow +2\text{NaCl}(\text{aq})$.

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18. Q198 CBSE 2024
    What ​is meant by a balanced chemical equation ​? Why is ​it necessary for the ​equation ​to be ​balanced ?
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    A balanced equation has equal atoms of each element on both sides, as mass is conserved in a chemical reaction.

    A balanced chemical equation is one in which the number of atoms of each element is the same on the reactant side and on the product side, for example $2\text{Mg}+{\text{O}}_2\to 2\text{MgO}$. An equation must be balanced because of the law of conservation of mass: mass can neither be created nor destroyed in a chemical reaction, so every atom present in the reactants must appear in the products.

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19. Q199 CBSE 2024
    Translate the following statements into chemical equations and then balance them :

    1. (i)Hydrogen sulphide gas burns ​in air to give ​water ​and sulphur dioxide.
    2. (ii)​Silver bromide on exposure to sunlight decomposes ​into ​silver ​and bromine.
    Show answer

    The balanced equations are $2{\text{H}}_2\text{S}+3{\text{O}}_2\to 2{\text{H}}_2\text{O}+2{\text{SO}}_2$ and $2\text{AgBr}\to 2\text{Ag}+{\text{Br}}_2$ in sunlight.

    (i) $2{\text{H}}_2\text{S}+3{\text{O}}_2\to 2{\text{H}}_2\text{O}+2{\text{SO}}_2$; (ii) $2\text{AgBr}\stackrel{\text{Sunlight}}{\to }2\text{Ag}+{\text{Br}}_2$

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20. Q200 CBSE 2024
    Write ​chemical equation for the chemical reaction ​which occurs ​when ​the aqueous solutions of barium chloride ​and sodium sulphate react together. Write ​the symbols of ​the ions present in ​the compound precipitated in the reaction.
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    The precipitate is barium sulphate, ${\text{BaSO}}_4$, which contains ${\text{Ba}}^{2+}$ and ${\text{SO}}_4^{2-}$ ions.

    ${\text{Na}}_2{\text{SO}}_4\text{(aq)}+{\text{BaCl}}_2\text{(aq)}\to {\text{BaSO}}_4\text{(s)}+2\text{NaCl(aq)}$. The precipitate is barium sulphate, ${\text{BaSO}}_4$, a white solid; the ions present in it are the barium ion, ${\text{Ba}}^{2+}$, and the sulphate ion, ${\text{SO}}_4^{2-}$.

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