Class 10 Science answer 2

Class 10 Science Chapter 1 Chemical Reactions and Equations Question-Answer

Class 10 Science Chapter 1 Chemical Reactions and Equations Question 1 to 11-Answer

1. Which of the statements about the reaction below are incorrect?

2PbO(s) + C(s) → 2Pb(s) + CO₂(g)

Lead is getting reduced.
Carbon dioxide is getting oxidised.
Carbon is getting oxidised.
Lead oxide is getting reduced.

(i) (a) and (b)

(ii) (a) and (c)

(iii) (a), (b), and (c)

(iv) all

Answer :-

The correct answer is:

(i) (a) and (b)

Explanation:

(a) Lead is getting reduced: This statement is incorrect. Lead oxide (PbO) is being reduced to lead (Pb), so lead is actually getting oxidized, not reduced.
(b) Carbon dioxide is getting oxidised: This statement is incorrect. Carbon dioxide (CO2) is a product of the reaction and is formed from the oxidation of carbon (C) to carbon dioxide. Therefore, carbon is getting oxidized.
(c) Carbon is getting oxidised: This statement is correct. Carbon (C) is indeed getting oxidized to carbon dioxide (CO2) during the reaction.
(d) Lead oxide is getting reduced: This statement is correct. Lead oxide (PbO) is indeed getting reduced to lead (Pb) during the reaction.

Therefore, the correct option is (i) (a) and (b), as these statements are incorrect.

2. Fe₂O₃ + 2Al → Al₂O₃ + 2Fe

The above reaction is an example of a

combination reaction.
double displacement reaction.
decomposition reaction.
displacement reaction.

The above reaction is an example of a:

(d) Displacement reaction.

Explanation:

In a displacement reaction, a more reactive element displaces a less reactive element from its compound. In the given reaction:

Fe₂O₃ + 2Al → Al₂O₃ + 2Fe

The aluminum (Al) is more reactive than iron (Fe). It displaces iron from iron oxide (Fe₂O₃), forming aluminum oxide (Al₂O₃) and elemental iron (Fe). Therefore, the reaction is a displacement reaction.

3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.

Hydrogen gas and iron chloride are produced.
Chlorine gas and iron hydroxide are produced.
No reaction takes place.
Iron salt and water are produced.

The correct answer is:

(a) Hydrogen gas and iron chloride are produced.

Explanation:

When dilute hydrochloric acid (HCl) is added to iron fillings (Fe), it reacts to form iron chloride (FeCl₂ or FeCl₃) and hydrogen gas (H₂). The general chemical equation for this reaction is:

2HCl + Fe → FeCl₂ (or FeCl₃) + H₂

Therefore, option (a) is the correct answer.

4. What is a balanced chemical equation? Why should chemical equations be balanced?

Answer

A balanced chemical equation is one in which the number of atoms of each element is the same on both the reactant and product sides of the equation. This balance ensures that the law of conservation of mass is upheld, meaning that matter is neither created nor destroyed in a chemical reaction.

Chemical equations should be balanced for several reasons:

Conservation of Mass: Balancing ensures that the total mass of the reactants equals the total mass of the products, which is a fundamental principle in chemistry known as the law of conservation of mass.
Stoichiometry: Balancing allows for accurate interpretation of the stoichiometry of a reaction. It ensures that the relative amounts of reactants and products are correctly represented.
Chemical Accuracy: A balanced equation accurately reflects the chemical composition and the ratio in which reactants combine and products form.
Predictive Purposes: Balanced equations provide information about the quantities of reactants needed and products formed, which is crucial for predicting the outcome of reactions in practical applications.
Chemical Understanding: Balancing equations promotes a deeper understanding of chemical reactions by revealing the specific ratios in which substances react and combine.

5. 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 sulphur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Answer

Here are the balanced chemical equations for the given statements:

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

3H₂ + N₂ → 2NH₃

(b) Hydrogen sulphide gas burns in air to give water and sulfur dioxide:

2H₂S + 3O₂ → 2H₂O + 2SO₂

3BaCl₂ + Al₂(SO₄)₃ → 2AlCl₃ + 3BaSO₄

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

2K + 2H₂O → 2KOH + H₂

These balanced chemical equations represent the reactions described in the statements, ensuring that the number of atoms of each element is the same on both sides of the equation.

6. Balance the following chemical equations.

(a) HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O
(b) NaOH + H₂SO₄ → Na₂SO₄ + H₂O
(c) NaCl + AgNO₃ → AgCl + NaNO₃
(d) BaCl₂ + H₂SO₄ → BaSO₄ + HCl

Answer

Here are the balanced chemical equations for the given reactions:

(a) HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O

[2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2H₂O]

(b) NaOH + H₂SO₄ → Na₂SO₄ + H₂O

[2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O]

[NaCl + AgNO₃ → AgCl + NaNO₃]

(d) BaCl₂ + H₂SO₄ → BaSO₄ + HCl

[BaCl₂ + H₂SO₄ → BaSO₄ + 2HCl]

These balanced equations ensure that the number of atoms of each element is the same on both sides of the equation.

7. 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) Aluminium + Copper chloride → Aluminium chloride + Copper
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

Answer

Here are the balanced chemical equations for the given reactions:

(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water

[Ca(OH)₂ + CO₂ → CaCO₃ + H₂O]

(b) Zinc + Silver nitrate → Zinc nitrate + Silver

[Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag]

[2Al + 3CuCl₂ → 2AlCl₃ + 3Cu]

(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

[BaCl₂ + K₂SO₄ → BaSO₄ + 2KCl]

These balanced equations ensure that the number of atoms of each element is the same on both sides of the equation.

8. Write the balanced chemical equation for the following and identify the type of reaction in each case.

(a) Potassium bromide(aq) + 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)

Answer

Here are the balanced chemical equations for the given reactions along with the identification of the type of reaction:

(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)

[2KBr(aq) + BaI₂(aq) → 2KI(aq) + BaBr₂(s)]

Type of reaction: Double displacement reaction

(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)

[ZnCO₃(s) → ZnO(s) + CO₂(g)]

Type of reaction: Decomposition reaction

[H₂(g) + Cl₂(g) → 2HCl(g)]

Type of reaction: Combination reaction

(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)

[Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)]

Type of reaction: Single displacement reaction

These balanced equations represent the given reactions and the type of reaction is identified based on the chemical changes that occur.

9. What does one mean by exothermic and endothermic reactions? Give examples.

Answer

Exothermic and Endothermic Reactions

Exothermic Reaction:

An exothermic reaction is one that releases heat energy to the surroundings.
In exothermic reactions, the products have less energy than the reactants, and the excess energy is released as heat.
Exothermic reactions usually feel warm to the touch.
Example: Combustion reactions, such as the burning of wood or the reaction between hydrogen gas and oxygen gas to form water, are exothermic. Another example is the reaction between sodium hydroxide and hydrochloric acid to form sodium chloride and water.

Endothermic Reaction:

An endothermic reaction is one that absorbs heat energy from the surroundings.
In endothermic reactions, the products have more energy than the reactants, and this energy is absorbed from the surroundings.
Endothermic reactions usually feel cool to the touch.
Example: Dissolving ammonium nitrate in water is an endothermic reaction because it absorbs heat from the surroundings, causing the temperature of the solution to decrease. Another example is the reaction between barium hydroxide octahydrate and ammonium chloride, which also absorbs heat from the surroundings.

In summary, exothermic reactions release heat energy to the surroundings, while endothermic reactions absorb heat energy from the surroundings.

10. Why is respiration considered an exothermic reaction? Explain.

Answer

Exothermic Nature of Respiration

Respiration is considered an exothermic reaction because it releases energy in the form of heat. During respiration, organic molecules such as glucose are broken down in the presence of oxygen to produce carbon dioxide, water, and energy in the form of ATP (adenosine triphosphate).

The overall chemical reaction for aerobic respiration, which occurs in cells, can be summarized as:

(C₆H₁₂O₆) + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)

In this reaction, glucose (C₆H₁₂O₆) reacts with oxygen (O₂) to produce carbon dioxide (CO₂), water (H₂O), and energy in the form of ATP. The breaking of chemical bonds in glucose molecules releases energy, which is then captured and stored in ATP molecules. This energy release is accompanied by the liberation of heat, making respiration an exothermic reaction.

Furthermore, since respiration is essential for providing energy to sustain life processes in organisms, the heat released during respiration helps maintain body temperature and supports various physiological functions. Therefore, respiration is considered an exothermic reaction due to the release of energy in the form of heat.

11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

Decomposition Reactions

Decomposition reactions are called the opposite of combination reactions because they involve the breakdown of a single compound into two or more simpler substances, whereas combination reactions involve the synthesis or formation of a single compound from two or more simpler substances.

In a decomposition reaction, a single reactant breaks down into two or more products. This is the opposite of a combination reaction, where multiple reactants combine to form a single product.

Here are the equations for these reactions:

Combination reaction:
2H₂(g) + O₂(g) → 2H₂O(l)
In this reaction, hydrogen gas (H₂) and oxygen gas (O₂) combine to form water (H₂O).

Decomposition reaction:
2H₂O(l) → 2H₂(g) + O₂(g)
In this reaction, water (H₂O) decomposes into hydrogen gas (H₂) and oxygen gas (O₂).

As shown in the examples, combination reactions involve the synthesis of a compound from simpler substances, while decomposition reactions involve the breakdown of a compound into simpler substances. This is why decomposition reactions are called the opposite of combination reactions.