Chapter U4.70, Problem 1TAI

Interpretation Introduction

Interpretation:

The classification of changes in matters must be explained.

Concept introduction:

Changes in matter can be either physical or chemical depending on the change in phase and formation of new substance respectively.

Answer to Problem 1TAI

Change in matteris classified as physical change and chemical change.

Dissolving is a special case which can be physical or chemical change.

Explanation of Solution

In some changes, new substances are generated with new properties and appearence. These changes are chemical change.

For example, when carbon is burnt in excesss oxygen, carbon dioxide is generated which has different properties with respect to both carbon and oxygen.

The reaction is represneted as follows:

  $C\left(s\right)+O_2\left(g\right)\to C{O}_2\left(g\right)$

Many dissolution processes are example of physical change in which no change in chemical properties takes place. For example, when sodium chloride is dissolved in water, then solid NaCl forms a homogeneous mixture in water via the formation of hydrated ions. The lattice energy of NaCl is overcomed by hydration energy of water.

For example, gold forms soluble complex ion with NaCN in presence of oxygen and water.

The reaction is represented as follows:

  $\text{Au}+\text{4NaCN}+{\text{O}}_{\text{2}}+{\text{2H}}_{\text{2}}\text{O}\to \text{2Na}\left[\text{Au}{\left(\text{CN}\right)}_{\text{2}}\right]+2\text{NaOH}+{\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$

Thus, it is a chemical change unlike other dissolution processes.

Conclusion

Thus changes in matter can be either physical or chemical change.