Chapter 14, Problem 13A

Interpretation Introduction

Interpretation: Implications of the fact that water expands on freezing has to be discussed.

Concept introduction: The measure of mass per unit volume of a substance is called as density. Density is given by the formula,

  $Density=\frac{Mass}{Volume}$

The density of solids is higher than liquids and gases because the molecules in solids are tightly/closely packed.

Answer to Problem 13A

The expansion of water upon freezing is important for aquatic life.

The expansion of water on freezing also causes pipes to burst and contribute to potholes in the road.

Explanation of Solution

In the process of freezing, water molecules lose energy and do not vibrate. This leads to formation of more stable hydrogen bonds between molecules, as there is less amount of energy of break the bond. Thus, water expands on freezing.

The volume of water expands when it freezes. It could otherwise be said as one gram of ice at ${\text{0}}^{\text{o}}\text{C}$ will have greater volume than one gram of liquid water at ${\text{0}}^{\text{o}}\text{C}\text{.}$ This is a significant implication. For example, in a confined space water could break its container when it freezes and expands. This causes the bursting of water pipes and engine blocks, which are unprotected in freezing weather.

The lower density of ice than density of liquid water makes it float on the surface of liquid water. Because, the ice expands on freezing, it occupies more space than water and serves as an insulation layer, which helps to prevent lakes and rivers from freezing solid in the winter. This signifies that aquatic life continues to have water in liquid state throughout the winter.

Conclusion

The expansion of water upon freezing is important for aquatic life.

The expansion of water on freezing also causes pipes to burst and contribute to potholes in the road.