Chapter 2, Problem 60A

Solution

(a)

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

The copper wire is bent.

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.

Physical change.

When a copper wire is bent, its physical appearance changes. There is no change in the chemical property of the copper wire. The chemical composition remains the same and no new compound is formed. Thus, when the copper wire is bent it is a physical change.

(b)

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

Burning of charcoal.

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.

Chemical change.

Burning of charcoal in a grill changes the chemical properties of charcoal. Due to combustion, it gets oxidized. Also, a combustion reaction is involved, thus, it is a chemical change.

Thus, the burning of charcoal in a grill is a chemical change. Here, the heat involved in combustion is a clue for chemical change.

(c)

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

Rise in bread dough after addition of yeast

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.

Chemical change.

The rise in bread dough when yeast is added is a chemical change. The reaction is known as fermentation. In this reaction, carbohydrate is consumed and carbon dioxide gas is released. This causes rises in the dough. The reaction is irreversible and it is a chemical change.

Here, a change in the shape of dough that cannot be reversed is a clue for a chemical change.

(d)

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

Sugar is dissolved in water.

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.

Physical change.

When sugar is dissolved in water, no change in the chemical composition of water takes place. Also, the process is reversible. As no new substance is formed, it is a physical change.