It is a cold, clear day in January. Brrrrrr. Tomorrow is your best friend's birthday and you are in a store buying a bouquet of helium-filled balloons to decorate your friend's locker. You pay the lady at the counter and laugh at the brightly colored balloons.

[ Do not inhale the helium, it is dangerous. We here at Aspire once knew a guy who inhaled some helium. His head popped off. ]

You begin the walk home in the crisp, cold air. Again, Brrrrrr. As you finish the last block before you are home you notice something wrong with the balloons! They have shrunk! That lousy store, they sold you defective balloons! Arrrgh!

Arrrgh!

[ Hey! Calm down... We here at Aspire are here to help. :) ]

But before you demand your money back, let's figure out why this happened.

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If we think about it, we already know some things about the "Mystery of the Deflating balloons" :
1. The balloons were inflated inside a warm store.

2. The balloons are filled with Helium, a gas.

3. Outside the store it is a "crisp, cold" day.

4. The pressure of the gas inside the balloon doesn't change.

We'd better use an experiment that will help us to understand how pockets of gas behave when they are exposed to changes in temperature.

In the 1700's, scientist Jacques Charles', conducted experiments with gas that led to his redesign of hot-air balloons as well as his appointment to the Académie des Sciences (Science Adcademy).

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Because we can't see gas particles, we here at Aspire have created a model in which particles have been magnified. (You're welcome.)

You should also be aware that we are only seeing a sliced-section of the space inside the tube and not all the gas particles are visible. The tube is closed off by a sliding plug.
:) This could be the inside of your lousy balloons.

1. Write down the independent variable (the variable YOU changed) and the dependent variable (the variable that changed because of the independent variable).

2. Predict how temperature might cause the balloons to change in volume. Write down your predictions.

3. To select a temperature, click on the thermometer and drag it to a different temperature.

4. The gas will be heated or cooled and, after any volume changes, you can record the data in the data table by clicking on the Record button.
   Important:
   Copy the data into your own lab notebook.

5. When you have sampled at least 6 temperatures, proceed to the analysis questions and the graphing section.

Do you realize you just used science to solve a problem? Cool beans.

[ We here at Aspire sometimes say "Cool Beans". ]

Scientists often test variables to find relationships. What variables were you testing in this lab? What changed? What stayed the same?

But wait- the fun isn't over yet. We still have some serious science to contemplate. How did your prediction match the data? Were you able to figure out what was going to happen?

Let's get back to the physics fun. Think about the experiment you just conducted. What happened when the temperature was raised? What happened when the temperature was lowered? In this experiment, what is the relationship between the temperature of a gas and the volume of the gas?



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• In a direct relationship, if one variable increases in value, the other variable also increases. (Eat more vegetables, build more muscles.)
• In an inverse relationship, if one variable increases, the other variable decreases. (Watch more TV, grades go down)

Is the relationship between temperature and volume direct or inverse?

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Here's a little scientific information for you. All gases are made up of molecules or atoms (particles). Particles are always in motion, either zipping around like you have seen, or vibrating in place. The hotter a gas gets, the faster the particles move.

Now that you have some background knowledge, explain why increasing the temperature of a gas would cause the volume of the gas to increase. Explain why decreasing the temperature would decrease the volume of the gas. Now relate this to your helium balloon mystery. What may have caused the balloons to decrease in volume?

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It is often valuable to analyze data by graphing the variables. Choose one of your experiments and make a graph of volume versus temperature. Usually the independent variable (the value you were able to select) goes on the horizontal axis. The dependent variable goes on the vertical axis. In this case, temperature will go on the X-axis and volume (which depended on temperature) will go on the Y-axis.

Scientists also use graphs to make predictions. Use your graph to predict answers to the following questions:


1. If you heat a gas to 120 C what volume will the gas have?

2. If you heat a gas to 73 C what volume will the gas have?

3. Predict what the volume of the gas would be at 160 C and -60 C. These numbers are not on the graph, but do the best you can.

For a challenge, look at another relationship found in your data. (Do this section if your teacher gives the okay.)

Draw a third column on your data table and label it V/T. For each of the rows in your data table divide the volume by the temperature and put that number in the new column. Did you get the same number each time? Did your neighbors get the same number each time? We call this number a constant.



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Because V/T is always a constant, one set of volume and temperature numbers will equal a second set of volume and temperature numbers:

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V1 and T1 represent the first set of conditions and V2 and T2 represent the second set of conditions.

This is only true if the numbers were collected at the same pressure. This relationship is called Charles' Law.

Practice a problem using the Charles' Law relationship:

If a gas is kept at a constant pressure and the volume is 10 L with a temperature of 25 C, what will the volume of the gas be if we change the temperature to 35 C?

When you are done, click on check answer to see how you did.


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Now try these questions:

1. If a gas with a volume of 15 L is at a temperature of 10 C, what is the volume if the temperature changes to 30 C?

2. If a gas with a volume of 25 L is at a temperature of 5 Kelvin, what is the temperature if the volume has changed to 40 L?

1. If a gas with a volume of 19 L is at a temperature of 29 Kelvin, what is the temperature if the volume has changed to 27 L?

2. If you were to place your inflated balloon in the warm oven for a few minutes, what would happen to it?

   [ We here at Aspire do not recommend eating your baked balloon. We here at Aspire think that is icky. :) ]

3. Why does a hot dog expand when it is heated over a fire? (It's not really gases, but it's a similar process.)

4. Okay, last question: why did your balloons deflate outside of the store?

That is quite the math workout. Congratulate yourself for your outstanding scientific abilities!