Chapter 2, Problem 94A

Interpretation Introduction

Interpretation: Whether physical changes are reversible or irreversible needs to be explained.

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

Whether a physical change is reversible or irreversible depends on the type of change taking place. Reversible change means the original substance can be obtained back after a physical change. On the other hand, in an irreversible change, the original substance cannot be obtained back. For example, the conversion of liquid water to ice on freezing is a physical change. Here, the state of water changes from liquid to solid. The liquid water can be obtained back by melting the ice. This is an example of reversible physical change.

An example of irreversible physical change is the grinding of wood into sawdust. Here, a wood block cannot be obtained back from the sawdust.