Chapter 2, Problem 46A

Interpretation Introduction

Interpretation: Four substances need to be identified that undergo a physical change if the temperature is reduced from $50{}^{\text{o}}\text{C}$ to $-50{}^{\text{o}}\text{C}$ . Also, the physical change in each case needs to be determined.

Concept Introduction: There are generally three states of matter that is solid, liquid and gas. Substances that are solid at room temperature have high melting and boiling points. Melting point is defined as the temperature at which a solid substance starts melting. The boiling point is defined as the temperature of a liquid when its vapor pressure is equal to the atmospheric pressure. This is the temperature when liquid starts to boil and convert into vapor.

Explanation of Solution

In table 2.1, the physical properties of some substances are given. The four substances which can undergo a physical change when the temperature is reduced from $50{}^{\text{o}}\text{C}$ to $-50{}^{\text{o}}\text{C}$ are chlorine, mercury, bromine, and water.

Here, chlorine is gas at room temperature and mercury, bromine, and water all are liquid at room temperature.

For chlorine, melting and boiling point is $-101{}^{\text{o}}\text{C}$ and $-34{}^{\text{o}}\text{C}$ respectively. Thus, chlorine will be gas in this range. When the temperature is $50{}^{\text{o}}\text{C}$ that is above its boiling point, it will be a gas. When the temperature is reduced to $-50{}^{\text{o}}\text{C}$ (less than boiling point but more than melting point), it gets converted into liquid.

Therefore, the change in physical state is from gas to liquid.

For mercury, melting and boiling point is $-39{}^{\text{o}}\text{C}$ and $357{}^{\text{o}}\text{C}$ respectively. Thus, the mercury will be liquid in this range. When the temperature is $50{}^{\text{o}}\text{C}$ that is less than its boiling point, it will be a liquid. When the temperature is $-50{}^{\text{o}}\text{C}$ that is less than its melting point, it will be solid.

Therefore, the change in physical state is from liquid to solid.

For bromine, melting and boiling point is $-7{}^{\text{o}}\text{C}$ and $59{}^{\text{o}}\text{C}$ respectively. Thus, bromine will be a liquid in this range. When the temperature is $50{}^{\text{o}}\text{C}$ that is below its boiling point, it will be a liquid. When the temperature is reduced to $-50{}^{\text{o}}\text{C}$ (less than a boiling point as well as a melting point), it gets converted into a solid.

Therefore, the change in physical state is from liquid to solid.

For water, melting and boiling point is $0{}^{\text{o}}\text{C}$ and $100{}^{\text{o}}\text{C}$ . Thus, water will be liquid in this range. When the temperature is $50{}^{\text{o}}\text{C}$ that is less than its boiling point, it will be a liquid. When the temperature is reduced to $-50{}^{\text{o}}\text{C}$ that is less than its melting point, it will be solid.

Therefore, the change in physical state is from liquid to solid.