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End of chapter exercises

Give one word or term for each of the following descriptions.

  1. The change in phase from a solid to a gas.

  2. The change in phase from liquid to gas.

a) Sublimation

 

b) Boiling.

Water has a boiling point of 100℃

  1. Define boiling point.

  2. What change in phase takes place when a liquid reaches its boiling point?

a) The temperature at which a liquid changes its phase to become a gas.

b) Liquid to gas.

Describe a solid in terms of the kinetic molecular theory.

A solid consists of atoms or molecules that have a low energy (vibrate around a fixed point). The particles are tightly packed together (there is very little space), there are strong attractive forces between the molecules. Solids have a fixed volume. Solids become liquids if their temperature is increased. In a few, rare cases solids become gases when their temperature is increased.

Refer to the table below which gives the melting and boiling points of a number of elements and then answer the questions that follow. (Data from http://www.chemicalelements.com)

Table 1

Element

Melting point (℃)

Boiling point (℃)

copper

1083

2567

magnesium

650

1107

oxygen

−218,4

−183

carbon

3500

4827

helium

−272

−268,6

sulphur

112,8

444,6

  1. What state of matter (i.e. solid, liquid or gas) will each of these elements be in at room temperature (25℃)?

  2. Which of these elements has the strongest forces between its atoms? Give a reason for your answer.

  3. Which of these elements has the weakest forces between its atoms? Give a reason for your answer.

a)

 

img_1.png

 

b) Carbon. It has the highest melting and boiling points. A high melting and boiling point indicates that a lot of energy is needed to overcome the forces holding the molecule together and so the higher the melting or boiling point, the stronger the forces.

c) Helium. It has the lowest melting and boiling points. A low melting and boiling point indicates that a small amount of energy is needed to overcome the forces holding the molecule together and so the lower  the melting or boiling point, the weaker the forces.

Complete the following submicroscopic diagrams to show what magnesium will look like in the solid, liquid and gas phase.

Figure 1
Image