Pure substances all behave about the same when they are gases. The Ideal Gas Law relates temperature, pressure, and volume of these gases in one simple statement: PV = nRT where P = pressure, V = volume, T = temperature, n = number of moles, and R is a constant.
When temperature increases, pressure and volume increase. Temperature is basically a speedometer for molecules. The faster they are wiggling and jiggling, the higher the temperature and the higher the thermal energy that object has. Pressure is how many pushes a surface feels from the motion of the molecules.
Materials: balloon, freezer, tape measure (optional)
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Hold a balloon in your hands and try to stuff it into a cup. Why is this so hard? You’re decreasing the volume and therefore increasing the pressure inside the balloon. (Since a balloon is so stretchy, this is near impossible to do without laughing.) You are compressing the balloon and thus increasing both the pressure and temperature inside the balloon slightly.
Blow up a balloon and stick it in the freezer overnight.
What happened? The balloon will shrink a bit because there is less pressure pressing on the inside of the balloon surface, holding the shape of the balloon. When you decrease temperature, the pressure and volume decrease as well.
Learn more about this scientific principle in Unit 13.
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Here’s a fun experiment take a bucket of dry ice and put bottled water in it and after a few hours banging it against a hard surface and watch
Good question! A pure substance is that one atom, element, or molecule all the way through, like diamonds, water, air, salt… Salt is NaCl (sodium and chloride atoms) which is a chemical compound, but is also a pure substance of salt . Do you see how all elements are pure substances?
I notice you use the phrase ‘pure substances.’ Is this the same as ‘element?’
Sounds like the temperature change wasn’t enough for you to see with your balloon. You can either make the air that you started with inside warmer (like do this on a hot day), or make the cold surrounding air colder, like with a block of dry ice in a cooler (get an adult to help you). You should see a change when you do one or both of these. When I do this with liquid nitrogen, the balloon shrinks down to its un-inflated size in the cooler, and when I bring it back out, it re-inflates right before your eyes!
Hello Aurora,
I did this experiment using a good quality balloon. The balloon was still the same the next day.
Why is that so?
Thank you!