Science & Technology · Chapter 15

27 solved questions

Chapter 15: Chemical Reaction

Every question in this chapter, answered and explained — step-by-step solutions drawn live from the chapter library across 7 question sections.

Very Short Answer Questions8 Short Answer Questions4 Give Reason Questions3 Differentiate Between2 Numerical / Equation-Based Problems5 Application / Conceptual Questions2 Additional SEE Practice3

Very Short Answer Questions

1SEE Boardqb-q0

What is a chemical reaction?

Ans.A chemical reaction is a process in which reactants change into new substances called products.

2SEE Boardqb-q1

What is a chemical equation?

Ans.A chemical equation is a chemical reaction written in the form of words, symbols, or chemical formulas of reactants and products.

3SEE Boardqb-q2

What is a combination reaction? Give one example.

Ans.A reaction in which two or more reactants combine to form only one product is a combination reaction. Example: 2Mg + O2 → 2MgO.

4SEE Boardqb-q3

What is a decomposition reaction? Give one example.

Ans.A reaction in which a reactant breaks down into two or more products is a decomposition reaction. Example: 2KClO3 → 2KCl + 3O2.

5SEE Boardqb-q4

What is a catalyst?

Ans.A catalyst is a substance which increases or decreases the rate of a chemical reaction without undergoing any permanent chemical change itself.

6SEE Boardqb-q5

Name one positive and one negative catalyst.

Ans.MnO2 is a positive catalyst; H3PO4 is a negative catalyst.

7SEE Boardqb-q6

What is the rate of a chemical reaction?

Ans.The change of reactants into products per unit time in a chemical reaction is called its rate.

8SEE Boardqb-q7

Write the general equation of an acid-base reaction.

Ans.Acid + Base → Salt + Water.

Short Answer Questions

1SEE Boardqb-q8

What is a displacement reaction? Write its types.

Ans.A reaction in which an atom or radical of one reactant is displaced by the atom or radical of another reactant is called a displacement reaction. Its two types are single displacement reaction and double displacement reaction.

2SEE Boardqb-q9

What is a neutralization reaction? Why is it called so?

Ans.A reaction in which an acid reacts with a base to form salt and water is called a neutralization reaction. It is called so because both the acid and base lose their properties and form a neutral compound (salt) and water.

3SEE Boardqb-q10

Write any four factors that affect the rate of a chemical reaction.

Ans.Catalyst, heat (temperature), pressure, and surface area are four factors that affect the rate of a chemical reaction. (Light is a fifth factor for reactions such as photosynthesis.)

4SEE Boardqb-q11

What is a positive catalyst and a negative catalyst?

Ans.A catalyst which increases the rate of reaction is called a positive catalyst, for example MnO2. A catalyst which decreases the rate of reaction is called a negative catalyst, for example H3PO4.

Give Reason Questions

1SEE Boardqb-q12

Why is hydrogen peroxide not stored in a transparent vessel?

Ans.Hydrogen peroxide decomposes faster in the presence of light. If stored in a transparent vessel, sunlight would reach it directly and increase its rate of decomposition, so it is stored in a coloured (opaque) vessel to protect it from light.

2SEE Boardqb-q13

Why is an acid-base reaction also known as a neutralization reaction?

Ans.In an acid-base reaction, both the acid and the base lose their individual properties as they react with each other and form a neutral salt and water. Because the acidic and basic properties are neutralized, it is called a neutralization reaction.

3SEE Boardqb-q14

Why is the rate of a chemical reaction different according to the type of reaction?

Ans.Different reactions involve different reactants, bond strengths, and conditions such as temperature, pressure, catalyst, surface area, and light. Because these factors vary from reaction to reaction, the rate at which reactants change into products also differs.

Differentiate Between

1SEE Boardqb-q15

a. Single and Double Displacement Reaction

Single Displacement Reaction	Double Displacement Reaction
Only one element or radical is displaced from a compound.	Two compounds mutually exchange atoms or radicals.
General form: AB + C → A + BC	General form: AB + CD → AD + CB
Example: Zn + H2SO4 → ZnSO4 + H2	Example: BaCl2 + Na2SO4 → BaSO4 + 2NaCl

2SEE Boardqb-q16

b. Combination and Decomposition Reaction

Combination Reaction	Decomposition Reaction
Two or more reactants combine to form one product.	One reactant breaks into two or more products.
General form: A + B → C	General form: AB → A + B
Example: N2 + 3H2 → 2NH3	Example: 2NaOH → Na2O + H2O

Numerical / Equation-Based Problems

1SEE Boardqb-q17

Balance and identify the type: KClO3 → KCl + O2.

Ans.Balanced equation: 2KClO3 → 2KCl + 3O2. Type: Decomposition reaction.

2SEE Boardqb-q18

Balance and identify the type: CH4 + O2 → CO2 + H2O.

Ans.Balanced equation: CH4 + 2O2 → CO2 + 2H2O. Type: Combination-type combustion reaction.

3SEE Boardqb-q19

Balance and identify the type: Fe + O2 → Fe2O3.

Ans.Balanced equation: 4Fe + 3O2 → 2Fe2O3. Type: Combination reaction.

4SEE Boardqb-q20

Balance and identify the type: Zn + H2SO4 → ZnSO4 + H2.

Ans.This equation is already balanced: Zn + H2SO4 → ZnSO4 + H2. Type: Single displacement reaction.

5SEE Boardqb-q21

Balance and identify the type: Al + H2SO4 → Al2(SO4)3 + H2.

Ans.Balanced equation: 2Al + 3H2SO4 → Al2(SO4)3 + 3H2. Type: Single displacement reaction.

Application / Conceptual Questions

1SEE Boardqb-q22

Four students A, B, C, and D carried out decomposition reactions differently: (i) A burnt magnesium ribbon, (ii) B mixed Zn in FeSO4 solution, (iii) C heated KClO3 in a hard glass test tube, (iv) D mixed Zn and HCl solution. Which student followed the correct procedure for a decomposition reaction? Write its balanced chemical equation.

Ans.Student C followed the correct procedure, since heating KClO3 is a decomposition reaction. Balanced equation: 2KClO3 --heat--> 2KCl + 3O2. (A's reaction is a combination reaction, B's and D's reactions are single displacement reactions, not decomposition.)

2SEE Boardqb-q23

Samir burns a magnesium ribbon. It burns brightly and forms a white ash 'A'. Write the name of substance 'A' and the balanced chemical equation of the process.

Ans.Substance 'A' is magnesium oxide (MgO). Balanced equation: 2Mg + O2 → 2MgO. This is a combination reaction.

Additional SEE Practice

1SEE Boardqb-q24

Identify the type of reaction: CaCO3 → CaO + CO2.

Ans.This is a decomposition reaction, since one reactant (CaCO3) breaks down into two products (CaO and CO2).

2SEE Boardqb-q25

Identify the type of reaction: NaCl + AgNO3 → AgCl + NaNO3.

Ans.This is a double displacement reaction, since NaCl and AgNO3 mutually exchange their radicals to form AgCl and NaNO3.

3SEE Boardqb-q26

Why does a powdered substance react faster than the same substance in solid lump form?

Ans.A powdered substance has a much larger surface area of contact than a solid lump of the same mass, so more particles are available to react at the same time, which increases the rate of reaction.

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