Chapter 2, Problem 78A

(a)

Interpretation Introduction

Interpretation: Whether the given change is physical or chemical needs to be determined.

Concept Introduction: When a substance changes its appearance or change in the state takes place and there is no change in its chemical composition, the change is said to be physical. On the other hand, when there is a change in the chemical composition of a substance or a new substance is formed after a chemical reaction, it is known as a chemical change.

Explanation of Solution

When plastic drinking bottles are burned to generate electricity, the chemical composition of plastic bottles is changed. Here, heat is generated also new species are formed; thus, it is a chemical change.

(b)

Interpretation Introduction

Interpretation: Whether the given change is physical or chemical needs to be determined.

Concept Introduction: When a substance changes its appearance or change in the state takes place and there is no change in its chemical composition, the change is said to be physical. On the other hand, when there is a change in the chemical composition of a substance or a new substance is formed after a chemical reaction, it is known as a chemical change.

Explanation of Solution

Digestion of a cereal bar is a chemical change. This is because several biological reactions take place in the digestion of food. These reactions are catalyzed by the enzyme. Since the process is irreversible and reactions are involved, it is a chemical change.

(c)

Interpretation Introduction

Interpretation: Whether the given change is physical or chemical needs to be determined.

Concept Introduction: When a substance changes its appearance or change in the state takes place and there is no change in its chemical composition, the change is said to be physical. On the other hand, when there is a change in the chemical composition of a substance or a new substance is formed after a chemical reaction, it is known as a chemical change.

Explanation of Solution

The evaporation of water is a physical change. In this change, water gets converted into vapor. Here, the physical state of water changes from liquid to vapor. Since only state changes and chemical composition remains the same, it is a physical change.

(d)

Interpretation Introduction

Interpretation: Whether the given change is physical or chemical needs to be determined.

Concept Introduction: When a substance changes its appearance or change in the state takes place and there is no change in its chemical composition, the change is said to be physical. On the other hand, when there is a change in the chemical composition of a substance or a new substance is formed after a chemical reaction, it is known as a chemical change.

Explanation of Solution

When a tomato is sliced for making a sandwich, its shape and size change but its chemical composition remains the same thus, it is a physical change.

(e)

Interpretation Introduction

Interpretation: Whether the given change is physical or chemical needs to be determined.

Concept Introduction: When a substance changes its appearance or change in the state takes place and there is no change in its chemical composition, the change is said to be physical. On the other hand, when there is a change in the chemical composition of a substance or a new substance is formed after a chemical reaction, it is known as a chemical change.

Explanation of Solution

Recycling plastic bottles involves many chemical reactions. Here, new products are formed and reactions are irreversible thus, it is a chemical change.