# Self Assessment and Practice

Fill in the blanks.  Then highlight the entire paragraph to reveal the answers.

The theory that explains the behavior of gases at the molecular level is called the kinetic theory, which is based on assumptions about a theoretical gas often referred to as an ideal gas.
Gases deviate most from ideal gas behavior under conditions of very low temperature and very high pressure.
The molecules of an ideal gas display no attraction or repulsion for one another.
Under ordinary conditions, an ideal gas consists chiefly of empty space, which explains why gases are so easily compressed.
Ideal gas particles travel in straight lines until they collide with each other or with the walls of their container.
The collisions between the molecules of an ideal gas are completely elastic.
The average kinetic energy of the molecules of an ideal gas is directly proportional to the Kelvin temperature of the gas.
A gas exerts pressure on the walls of its container because gas molecules collide with the walls of the container. So, the pressure exerted by a gas depends on two factors:
a) the number of collisions that occur
b) the energy of the collisions/the force with which the molecules hit the walls of the container
To measure gas pressure, an instrument called a manometer is used.
The Earth’s atmosphere has weight, which creates atmospheric pressure.
The instrument used to measure atmospheric pressure is the barometer.
Standard Temperature and Pressure (or STP ) is:
273 K 101.3 kPa 1.0 atm
0 °C 760 mm Hg 760 torr
At 1 atm, the height of the mercury in a barometer is 760 mm.

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Use the kinetic theory to explain why a helium filled balloon “shrinks” when it is taken from a warm room to the outside on a cold day.

Pressure remains constant in this scenario. (It is assumed that atmospheric pressure is the same inside the warm room as outside!) Decreasing the temperature of a gas means that the particles have less kinetic energy. Consequently, the collisions of the gas molecules with the walls of the container occur less often and are not as forceful, so the gas pressure would decrease. In order for pressure to remain constant (which it must, since atmospheric pressure is constant), the volume of the balloon must decrease.

Use the kinetic theory to explain why bubble wrap pops when it is squeezed.

When the bubble is squeezed, the gas is forced into a smaller volume. If the same amount of gas is in less space, there are more particles per unit volume, causing more collisions with the walls of the container. Because the collisions the gas particles have with the walls of the container are what cause gas pressure, more collisions mean greater pressure. The pressure is greater than the strength of the bubble wrap, and so the bubble wrap pops.

When the bubble is squeezed, the gas is forced into a smaller volume. If the same amount of gas is in less space, there are more particles per unit volume, causing more collisions with the walls of the container. Because the collisions the gas particles have with the walls of the container are what cause gas pressure, more collisions mean greater pressure. The pressure is greater than the strength of the bubble wrap, and so the bubble wrap pops.

Use the kinetic theory to explain why tire pressure increases when more aire is added to a tire.

Adding more gas particles to a container increases the gas pressure because there are more gas particles hitting the walls of the container. According to the kinetic theory, these collisions with the walls of the container are what cause gas pressure. More collisions means more pressure.

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