Gas Laws (Sohail Bhatri)

Title: Gas Laws

Principle(s) Investigated:

Boyle's Law, Charles' Law and combined gas law.

Standards:

HS-PS1-5: Apply scientific principles and evidence to provide an explanation about the effects of changing the

temperature or concentration of the reacting particles on the rate at which a reaction occurs.

Materials:

1) Erlenmeyer Flask

2) Balloon

3) Ice and Water.

4) Hot/boiling water.

5) Tongs

Procedure:

Place about 20 ml of water in the flask and boil it.
Place a balloon over the flask and remove the flask from the heat
Place the flask/balloon set up in an ice bath
As it cools, have students write down observations at to what happens( The balloon should get pushed into the flask and inflate while inside the flask)

Student prior knowledge: Students should understand that matter is anything that has mass and takes up space. Student should also understand that volume is the amount of space an object takes up. Pressure is the amount of collisions between molecules and the walls of the container and that temperature is the measure of average kinetic energy of a substance.

Explanation: As the water molecules are heated, the molecules in the air and water speed up and spread out. They begin to occupy more space since the flask is open to the environment. When the balloon is placed on the flask, the system is no longer open to the air and a closed system. When the balloon and the flask cool, the molecules inside of the container begin to move slower and take up less space. This lowers the pressure inside of the balloon and flask. When the pressure inside the balloon drops below atmospheric pressure, it is pushed inside the flask and inflates inside the flask. This could be used as an introduction to all of the gas laws.

Boyle's Law:

Charles' Law:

Combined Gas Law:

Questions & Answers:

What causes the balloon to get pushed into the flask and expand in the flask? There is a pressure gradient that is caused due to the cooling of molecules inside of the flask which leads to the balloon being pushed into the flask. Since the water and air particles are rapidly cooled, the volume it occupies decreases which lowers the pressure inside the flask and causes the gradient

Can this process be reversed? Explain how that would be possible. This process can be reversed by simply increasing the temperature of the molecules inside the flask. As the temperature of the liquid increases, the pressure inside of the flask increases. When the pressure inside of the flask is greater than the atmospheric pressure, the balloon will be pushed back out.
What real world applications does this demonstration help explain? This demonstration can explain how hot air balloons work. When the air in a hot air balloon is heated, the air expands the volume decreases. Since the volume is defined as mass/volume, a larger volume means a lower density which causes the hot air balloon to float. This demonstration also explains the fluctuations in tire pressure during summer and winter months. During summer, the temperature is higher so the air pressure is also higher. As the temperature cools down, the air pressure will also decrease.

Applications to Everyday Life:

Hot Air Balloons: This demonstration can explain how hot air balloons work. When the air in a hot air balloon is heated, the air expands the volume decreases. Since the volume is defined as mass/volume, a larger volume means a lower density which causes the hot air balloon to float.
Mechanics of breathing: Your diaphragm pulls down expanding your chest cavity and thus reducing the pressure inside the cavity. Since the pressure inside is lower than atmospheric pressure, air is pushed into your lungs. When your diaphragm relaxes, the space in your chest cavity decreases, thus increasing the pressure above atmospheric pressure and driving air back out of your lungs.
Air pressure fluctuations in car tires: The air pressure inside the tire is influenced by the environmental temperature. When the temperature is high outside, the air pressure inside the tire increases as the molecules are heated up and move faster. When the temperature drops due to daily or seasonal shifts, the air pressure inside the tire decreases due to particles moving slower.

Photographs: