GED Science Practice Test: Properties of Gases and the Gas Laws

The idea of energy was introduced as we learned about phase changes in the previous section.  Three observable properties of gases that are influenced by energy include temperature, pressure, and volume.  Three main gas laws describe the energy and relationships among temperature, pressure, and volume.

Charles’ Law:  This gas law describes the relationship between the temperature and volume of a gas.  As a gas increases in temperature, its particles move with higher speed and energy and take up more space.  Charles’ Law describes a direct relationship.  A direct relationship is one in which both quantities go in the same direction (e.g., temperature up, volume up).

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Boyles’ Law:  This gas law describes the relationship between the pressure and volume of a gas.  As the pressure on a gas increases, its volume decreases. In other words, the pressure compresses the particles in a gas into a smaller space. Boyles’ Law describes an inverse relationship. An inverse relationship is one in which the two quantities go in opposite directions (e.g., pressure up and volume down).  The following diagram shows a graph of this inverse relationship, along with pictures showing the pressure and volume:

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Gay-Lussac’s Law:  This gas law describes the relationship between the pressure and temperature of a gas.  As the pressure on a gas increases, its temperature also increases.  As pressure compresses gas particles into a smaller space, more collisions can occur between gas particles, which increases their temperature.

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The gas laws describe observable properties of gases.  One can describe these observable properties in terms of what happens at the atomic level within those gases.  The description of gas (fluid) behavior at a molecular level is called kinetic molecular theory, and is made of five parts:

  1. Gas particles move in a straight line until they collide with another particle or the walls of the container.
  2. Gas particles are much smaller than the distance between particles. Most of the volume of a gas is therefore empty space.
  3. There is no force of attraction (or repulsion) between gas particles or between the particles and the walls of the container.
  4. Energy of gas particles is not lost when it collides with another particle or with the walls of the container.
  5. The average kinetic energy of a collection of gas particles depends on the temperature of the gas and nothing else.

 

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