GED Science Test: The Characteristics of Matter - dummies

GED Science Test: The Characteristics of Matter

By Murray Shukyn, Achim K. Krull

The GED Science test will have some questions dealing with the characteristics of matter. Every type of matter has certain characteristics that distinguish it from other types, including how hard it is, its melting and freezing points, how reactive it is with other types of matter, and so on. Here, you explore the various characteristics of matter.

Physical properties

Physical properties of matter are those that can be observed and measured without changing the nature of the matter. These properties are categorized as intensive and extensive:

  • Intensive properties are those that don’t depend on the amount of matter, including color, odor, luster, malleability, ductility, conductivity, hardness, melting/freezing/ boiling points, and density (mass per unit volume).

  • Extensive properties depend on the amount of matter and include mass, weight, volume, and length.

Chemical properties

Chemical properties can be seen and measured only when matter undergoes a chemical change or reaction. Chemical properties include reactivity, toxicity, flammability (how easily a substance ignites), heat of combustion (the amount of energy released when a substance is burned in the presence of oxygen), and half-life (the amount of time for half of the original substance to decay).

Changes of state

Common physical properties that scientists often study and refer to are changes of state, when a substance changes from its solid to its liquid form or from its liquid to its gas form or vice versa. These changes of state occur at certain points relative to pressure and temperature.

For example, water generally turns from a liquid into a solid (ice) at 0°C or 32°F and from water to gas (steam) at 100°C or 212°F. Changes in pressure affect the melting and (even more so) the boiling point of water.

Changes of state occur when energy is added or removed. Generally speaking, when energy is added to a substance, the motion of the molecules and the distance among molecules increases, and when energy is removed from a substance, the motion of the molecules and the distance among them decreases.

The word “generally” is used here because mostly because water doesn’t comply; when it changes from water to ice, the distance among molecules actually increases because of the way water molecules are structured when they crystallize. For most substances, the solid is denser (less volume) than the liquid form.

Scientists commonly use a heating curve to represent a substance’s changes of state. The image below shows the heating curve for water. Note that the curve flattens at the melting point of 0°C and boiling point of 100°C. At these points, energy is added without causing a rise in temperature because the energy is being used to fuel the change of state.

Heating curve for water.
Heating curve for water.

Changes of state occur in either direction. Adding heat, for example, changes water from a solid (ice) to a liquid (water) to a gas (steam). Removing heat changes water from a gas to a liquid through condensation and from a liquid to a solid through freezing.

Some substances change directly from a gas to a solid, skipping the liquid phase (a process referred to as deposition) and change directly from a solid to a gas (sublimation). Solid carbon dioxide (dry ice), for example, passes from a solid into a gas.

  1. Which of the following processes occurs when a solid turns directly into a gas?

    • (A) melting

    • (B) condensation

    • (C) vaporization

    • (D) sublimation

  2. Which of the following most clearly describes the difference between boiling and evaporation?

    • (A) There is no difference.

    • (B) Boiling breaks the bonds between atoms, while evaporation does not.

    • (C) When a liquid boils, its temperature remains constant, while evaporation may occur at different temperatures.

    • (D) During evaporation, temperature remains constant, while boiling may occur at different temperatures.

Check your answers:

  1. When a solid skips the liquid stage and turns directly into a gas, the process is called sublimation, Choice (D).

  2. As shown, water boils at a constant temperature as it turns from a liquid into a gas, but the temperature of the steam (droplets of water) can continue to rise. Choice (C) is correct.