Chapter 3, Problem 49A

Interpretation Introduction

Interpretation:

Difference between a physical change and a chemical change needs to be explained.

Concept introduction:

The nature of any substance is explained by their chemical properties and physical properties.

Answer to Problem 49A

A physical change modifies a substance without changing its composition, while a chemical change involves a change in composition.

Explanation of Solution

A physical property describes the physical changes of a substance. Physical change is a temporary change; it is a reversible change. For example, color, mass, volume, etc.

A chemical property describes how a substance reacts with other substances. In a chemical change, a new substance is formed and absorption of energy or loss of energy occurs; it is an irreversible change. For example, rusting, dissolving, etc.

The difference between the physical and a chemical change is mentioned below:

Properties	Physical change	Chemical change
The types of changes	In the physical changes, the change is for a short duration.	These changes are permanent.
Absorption of heat	There is very little quantity of heat is absorbed for the change in the position of the atoms.	In chemical changes absorption and evolution of heat take place. More energy requires the breaking of the chemical bond in a chemical reaction.
Reversibility of reaction	The physical changes are reversible, there is only phase transfer take place.	The chemical changes are irreversible.
Energy production	In the physical changes, no production of energy takes place.	In the chemical changes, the energy produces in the form of light, heat, etc.

Conclusion

The physical and chemical changes are different from each other. In the physical changes, no new substance is formed and the ratio of composition remains unchanged while in the chemical changes new product is formed with variation in the composition of the product from the reactant of a chemical reaction.