CBSE Class 10 Science Chapter 1: Chemical Reactions and Equations NCERT Solutions

The correct option is (i) (a) and (b).

Let's analyze the given reaction: $2\; \backslash text\{PbO\}\_\{(s)\}\; +\; \backslash text\{C\}\_\{(s)\}\; \backslash longrightarrow\; 2\; \backslash text\{Pb\}\_\{(s)\}\; +\; \backslash text\{CO\}\_\{2(g)\}$

Oxidation is the gain of oxygen or loss of electrons, while reduction is the loss of oxygen or gain of electrons.

In this reaction:

• Lead oxide (PbO) loses oxygen to form lead (Pb). Therefore, lead oxide is reduced. Statement (d) is correct.
• Carbon (C) gains oxygen to form carbon dioxide (CO2). Therefore, carbon is oxidised. Statement (c) is correct.
• Since lead oxide is reduced, statement (a) 'Lead is getting reduced' is incorrect because it is the compound (lead oxide) that is reduced, not just the element lead in isolation.
• Since carbon is oxidised to carbon dioxide, statement (b) 'Carbon dioxide is getting oxidised' is incorrect. Carbon dioxide is the product of oxidation, not the substance being oxidised.

Thus, the incorrect statements are (a) and (b).

The correct option is (d) displacement reaction.

In this reaction, Aluminium (Al) is more reactive than Iron (Fe). Aluminium displaces Iron from its oxide (Fe2O3) to form Aluminium oxide (Al2O3) and Iron (Fe). This type of reaction, where a more reactive element displaces a less reactive element from its compound, is called a displacement reaction.

The correct answer is (a) Hydrogen gas and iron chloride are produced.

When iron (Fe) reacts with dilute hydrochloric acid (HCl), a chemical reaction occurs. Iron is a metal that reacts with acids to produce a salt and hydrogen gas. In this case, iron reacts with hydrochloric acid to form iron(II) chloride (FeCl2) and hydrogen gas (H2).

The balanced chemical equation for this reaction is:

$$Fe\_\{(s)\}\; +\; 2HCl\_\{(aq)\}\; \backslash longrightarrow\; FeCl\_\{2(aq)\}\; +\; H\_2\; \backslash uparrow$$

Therefore, hydrogen gas and iron chloride are produced.

A balanced chemical equation is a representation of a chemical reaction where the number of atoms of each element is identical on both the reactant side and the product side of the equation. This ensures that the total number of atoms for each element remains the same before and after the reaction.

Chemical equations must be balanced due to the fundamental principle of the Law of Conservation of Mass. This law states that matter can neither be created nor destroyed during a chemical reaction. Consequently, the total mass of the reactants consumed must be equal to the total mass of the products formed. Balancing the equation ensures that the number of atoms of each element is conserved throughout the reaction, thereby satisfying the law of conservation of mass.

Here are the balanced chemical equations for the given statements:

(a) Hydrogen gas combines with nitrogen to form ammonia.

The reactants are hydrogen gas ($H\_2$) and nitrogen gas ($N\_2$). The product is ammonia ($NH\_3$).

Unbalanced equation: $H\_2\; +\; N\_2\; \backslash longrightarrow\; NH\_3$

Balanced equation: $$3H\_\{2(g)\}\; +\; N\_\{2(g)\}\; \backslash longrightarrow\; 2NH\_\{3(g)\}$$

(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.

The reactants are hydrogen sulphide gas ($H\_2S$) and oxygen from air ($O\_2$). The products are water ($H\_2O$) and sulphur dioxide ($SO\_2$).

Unbalanced equation: $H\_2S\; +\; O\_2\; \backslash longrightarrow\; H\_2O\; +\; SO\_2$

Balanced equation: $$2H\_2S\_\{(g)\}\; +\; 3O\_\{2(g)\}\; \backslash longrightarrow\; 2H\_2O\_\{(l)\}\; +\; 2SO\_\{2(g)\}$$

(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.

The reactants are barium chloride ($BaCl\_2$) and aluminium sulphate ($Al\_2(SO\_4)\_3$). The products are aluminium chloride ($AlCl\_3$) and barium sulphate ($BaSO\_4$).

Unbalanced equation: $BaCl\_2\; +\; Al\_2(SO\_4)\_3\; \backslash longrightarrow\; AlCl\_3\; +\; BaSO\_4$

Balanced equation: $$3\; \backslash text\{BaCl\}\_\{2(aq)\}\; +\; \backslash text\{Al\}\_2\; (SO\_4)\_\{3(aq)\}\; \backslash longrightarrow\; 2\; \backslash text\{AlCl\}\_\{3(aq)\}\; +\; 3\; \backslash text\{BaSO\}\_\{4(s)\}$$

(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

The reactants are potassium metal (K) and water ($H\_2O$). The products are potassium hydroxide (KOH) and hydrogen gas ($H\_2$).

Unbalanced equation: $K\; +\; H\_2O\; \backslash longrightarrow\; KOH\; +\; H\_2$

Balanced equation: $$2K\_\{(s)\}\; +\; 2H\_2O\_\{(l)\}\; \backslash longrightarrow\; 2KOH\_\{(aq)\}\; +\; H\_\{2(g)\}$$