Chapter 7, Problem 98A

(a)

Interpretation Introduction

Interpretation: The baking of cookies needs to be identified as a chemical or physical change.

Concept Introduction: In any physical change, the appearance of matter changes but the kind of matter remains the same. For example, in the freezing of water; here, the physical property of water changes from liquid to solid but the chemical property remains the same that is the formula of water remains ${\text{H}}_{\text{2}}\text{O}$ . In a chemical change, the chemical composition of matter changes. In this change, a new substance is formed. For example, the reaction of hydrogen and oxygen to form ${\text{H}}_{\text{2}}\text{O}$ .

Answer to Problem 98A

Chemical change.

Explanation of Solution

When cookies are baked, different ingredients are mixed such as flour, sugar, oil, milk, etc. Here, the appearance of matter changes as well as the chemical properties. Also, baking involves heating; thus, it is a chemical change.

(b)

Interpretation Introduction

Interpretation: The light emitted by a firefly needs to be identified as a chemical or physical change.

Concept Introduction: In any physical change, the appearance of matter changes but the kind of matter remains the same. For example, in the freezing of water; here, the physical property of water changes from liquid to solid but the chemical property remains the same that is the formula of water remains ${\text{H}}_{\text{2}}\text{O}$ . In a chemical change, the chemical composition of matter changes. In this change, a new substance is formed. For example, the reaction of hydrogen and oxygen to form ${\text{H}}_{\text{2}}\text{O}$ .

Answer to Problem 98A

Chemical change.

Explanation of Solution

A firefly emits light due to a chemical reaction taking place in its abdomens. This reaction is caused by an organic compound luciferin. The process is known as bioluminescence. In this reaction, luciferin combines with oxygen, calcium, and ATP in the presence of luciferase to form a bioluminescent enzyme. Since it occurs due to a chemical reaction, it is a chemical change.

(c)

Interpretation Introduction

Interpretation: The carving of a figure from wood needs to be identified as a chemical or physical change.

Concept Introduction: In any physical change, the appearance of matter changes but the kind of matter remains the same. For example, in the freezing of water; here, the physical property of water changes from liquid to solid but the chemical property remains the same that is the formula of water remains ${\text{H}}_{\text{2}}\text{O}$ . In a chemical change, the chemical composition of matter changes. In this change, a new substance is formed. For example, the reaction of hydrogen and oxygen to form ${\text{H}}_{\text{2}}\text{O}$ .

Answer to Problem 98A

Physical change.

Explanation of Solution

When a figure is carved from wood, it does not change the properties of the wood. The chemical nature of wood remains the same only the appearance changes thus, it is a physical change.

(d)

Interpretation Introduction

Interpretation: The making of caramel from sugar needs to be identified as a chemical or physical change.

Concept Introduction: In any physical change, the appearance of matter changes but the kind of matter remains the same. For example, in the freezing of water; here, the physical property of water changes from liquid to solid but the chemical property remains the same that is the formula of water remains ${\text{H}}_{\text{2}}\text{O}$ . In a chemical change, the chemical composition of matter changes. In this change, a new substance is formed. For example, the reaction of hydrogen and oxygen to form ${\text{H}}_{\text{2}}\text{O}$ .

Answer to Problem 98A

Chemical change.

Explanation of Solution

Caramel is made from sugar by heating sugar with water. Converting sugar to caramel is known as the caramelization reaction. In this reaction oxidation of sugar takes place by heating. Since heating is involved, it is a chemical change.