Chapter 24, Problem 99A

(a)

Interpretation Introduction

Interpretation:

The process that occurs in a solid air freshener cube getting smaller and smaller should be explained.

Concept introduction:

Any change is either physical or chemical. A physical change brings about a change in the physical property of an object and not its composition. On the other hand chemical change brings about change in composition of object. It is also called chemical reaction.

Answer to Problem 99A

The process that occurs in a solid air freshener cube getting smaller and smaller is sublimation.

Explanation of Solution

Change in state of a compound from solid to gas, without going through liquid phase is sublimation. It is a process where only state/ phase changes but composition remains same.

The process that occurs in a solid air freshener cube getting smaller and smaller is sublimation.

(b)

Interpretation Introduction

Interpretation:

The process that occurs in formation of dew drops on leaves in morning should explained.

Concept introduction:

Any change is either physical or chemical. A physical change brings about a change in the physical property of an object and not its composition. On the other hand chemical change brings about change in composition of object. It is also called chemical reaction.

Answer to Problem 99A

The process that occurs in formation of dew drops on leaves in morning is condensation.

Explanation of Solution

Change in state of a compound from gaseous state to liquid state is condensation. In air moisture is also present which condense into droplets when temperature is low or coming in contact of cool surface of leaves and glass, especially in winter mornings.

The process that occurs in formation of dew drops on leaves in morning is condensation.

(c)

Interpretation Introduction

Interpretation:

The process that occurs in steam rising from hot spring should be identified.

Concept introduction:

Any change is either physical or chemical. A physical change brings about a change in the physical property of an object and not its composition. On the other hand chemical change brings about change in composition of object. It is also called chemical reaction.

Answer to Problem 99A

The process that occurs in steam rising from hot spring is evaporation.

Explanation of Solution

Evaporation is process of conversion of liquid into gas phase. In hot spring, water when reaches its boiling temperature, gets converted into steam.

Hence, the process that occurs in steam rising from hot spring is evaporation.

(d)

Interpretation Introduction

Interpretation:

The process that occurs in crust of ice forming on top of pond should be identified.

Concept introduction:

Any change is either physical or chemical. A physical change brings about a change in the physical property of an object and not its composition. On the other hand chemical change brings about change in composition of object. It is also called chemical reaction.

Examples of physical change are: change in state like evaporation, condensation, change in color or shape. Examples of chemical change are: combustion, decomposition reactions.

Answer to Problem 99A

The process that occurs in crust of ice forming on top of pond is freezing.

Explanation of Solution

Freezing is process of conversion of liquid into solid phase. The temperature of water when lowers to or more than $0^{°}\text{C}$, process of freezing begins.

Hence, the process that occurs in crust of ice forming on top of pond is freezing.