Chapter 6, Problem 85A

(a)

Interpretation Introduction

Interpretation: To identify ‘melting of iron’ a physical change or chemical change

Concept introduction:

When one chemical substance is converted into one or more distinct chemicals, this is known as a chemical transformation. Physical change is defined as a typically reversible alteration of a substance's physical characteristics, such as its size or shape.

Answer to Problem 85A

Physical change

Explanation of Solution

In the melting of iron, no new substance is formed only the state of the substance is changed. A solid iron rod is converted into a liquid state and this process is reversible also.

Thus, the melting of iron is a physical process.

(b)

Interpretation Introduction

Interpretation: To identify ‘lighting a match’ a physical change or chemical change

Concept introduction:

When one chemical substance is converted into one or more distinct chemicals, this is known as a chemical transformation. Physical change is defined as a typically reversible alteration of a substance's physical characteristics, such as its size or shape.

Answer to Problem 85A

Chemical change

Explanation of Solution

In the lighting of a match, a chemical reaction occurs. Heat is produced because of friction when rubbing the matchstick's head against the striking surface. A small portion of the red phosphorus chain is broken by this heat. Some red phosphorus then turns into white phosphorus after that. White phosphorus is a chemical that ignites in the air and is extremely volatile.

Thus, lighting a match is a chemical process.

(c)

Interpretation Introduction

Interpretation: To identify ‘grinding a corn’ a physical change or chemical change

Concept introduction:

When one chemical substance is converted into one or more distinct chemicals, this is known as a chemical transformation. Physical change is defined as a typically reversible alteration of a substance's physical characteristics, such as its size or shape.

Answer to Problem 85A

Chemical change

Explanation of Solution

Physical change is reversible while chemical change is irreversible. When corn is ground, it changes into a powder form which cannot be converted back to corn.

Thus, grinding corn is a chemical change.

(d)

Interpretation Introduction

Interpretation: To identify ‘souring of milk’ a physical change or chemical change

Concept introduction:

When one chemical substance is converted into one or more distinct chemicals, this is known as a chemical transformation. Physical change is defined as a typically reversible alteration of a substance's physical characteristics, such as its size or shape.

Answer to Problem 85A

Chemical change

Explanation of Solution

Physical change is reversible while chemical change is irreversible. The Souring of milk is a chemical change. Because lactic acid is produced due to milk sourness, it is referred to be a chemical change.

Thus, ‘souring of milk’ is a chemical change.