Here is an experiment that even the professionals at AstroCamp will not dare to perform. Water can become superheated in a closed system, like that in a microwave, and become extremely dangerous. Superheated water is liquid water under pressure at temperatures between the usual boiling point, 100 °C, and the critical temperature, 374 °C.
Superheated water can be stable because the liquid water is in equilibrium with the vapor. However, if water becomes superheated due to this equilibrium and a lack of bubbles or impurities, then it will all of a sudden boil if there is a change in the system. This could be a simple as jostling the liquid, introducing something like a spoon, tea bag, or even a tiny piece of dust!
Smooth containers do not have bubbles of air clinging to their sides. Rough or scratched containers may hold microscopic bubbles in their cracks, becoming nuclei for boiling. These nuclei provide a source for the water to release heat and energy in a safe way. But with a smooth container, when a nuclei is added, the superheated water will explode!
I’ll be honest: This one blew me away the first time I saw it! What is going on here? It all has to do with polymers, which are basically long chains of repeated molecules, which you can learn more about here.
Just to re-iterate: This is not dangerous to you, but it is dangerous to the microwave!
These polymers have some interesting properties that we need to understand, and then this will become much simpler. As we have seen before, temperature can be an important part of chemistry. That is also important here! Let’s start by talking about something a more familiar polymer: protein!
We all have lots of protein in our bodies which perform many different functions. These functions are determined by their shapes, which are in turn determined by the specific molecules that make them up. However, if proteins are exposed to high temperatures or acidic conditions, they lose their shape and just uncoil into a big mess. This is called denaturation, is actually a good thing for us. Human stomachs are highly acidic, and when you eat food with protein in it, this allows the protein to be broken down so that it can be used.
A similar thing happens with the polymers in the bag*. When these huge chains are hot, they become very flexible. Left to their own devices, they will tangle up and clump into a polymer mess. Alternatively, in this flexible state they can be easily manipulated a different shape. When they are cooled down, they maintain this shape.
This gives us all the tools we need to understand the behavior of these bags in the microwave. These bags contain a polymer skeleton surrounded with foil and paint. When the bags are manufactured, they are heated up and stretched out before being cooled off. The result is that the long polymers in the bag are locked into long straight lines forming the structure of the bag.
In the microwave, they get HOT. Without anything to hold them in position, they collapse into their natural shape: a big clump. As the bag’s polymer skeleton collapses, the bag itself shrinks dramatically. The results are astounding!
Written By: Scott Alton
*Note: If you are reading carefully, it may seem like this is the exact opposite of the protein. This is because proteins are heated up to the point where they collapse to the appropriate shape at body temperature, whereas for these polymers that temperature is much higher. If these polymers were to get even hotter, they would exhibit similar denaturation behavior. Similarly, cooling the protein well below body temperature would lock them into their current shape. The same thing is happening, it is just on different temperature scales.
Woah! What just happened? To try and understand it, lets take a closer look at the Microwave. These are often thought of as magic food reheating boxes, but they are actually quite interesting!
Microwave ovens heat food by bombarding it with electromagnetic radiation, also known as light. Unlike the light most of us think of when we use that word, microwave light is invisible. All light travels in the form of waves, and these particular waves are stretched out too much for the human eye to detect.
This animation shows how an electomagnetic wave travels. It is actually two interconnecting waves, one electric and one magnetic. Source Dr. Hans Fuchs, Georg-August-Universität Göttingen
Eyes are great for detecting light, but they can only detect certain wavelengths of it. Most light is actually outside the realm of the human eye! Scientists often build telescopes to look at these other kinds of light like ultraviolet, x-ray, infrared, and even microwaves to see what it is that we are missing when looking at the sky with just our eyes.
Different types of light make up the electromagnetic spectrum and are separated by their wavelength. The visible spectrum makes up a tiny portion of it. Image from NASA
Microwaves are also the perfect length for transferring heat energy to food. As the electromagnetic waves move through it, they bend the polar molecules (molecules that have positively charged and negatively charged ends)! As the molecules wiggle in microwaves, they bump into one another and speed each other up. Temperature is really just a way to measure how fast the molecules in something are moving, so as the molecules wiggle faster and faster, the food heats up! Just as importantly, they also heat up any pockets of gas that are trapped inside of whatever we’re trying to warm.
Ivory soap contains a huge number of microscopic air bubbles. When the microwave oven begins heating, two important things happen: the soap itself softens and melts, and the air trapped inside the soap expand.
This is due to Charles’s Law, discussed here. Ultimately, the tiny air pockets in the Ivory soap grow into a giant froth of bubbles. You may have seen this process before… it’s the same science that causes popcorn to morph from small, dense kernels into fluffy, bite-sized chunks!
Popcorn kernel popping. Source 9gag.
So, have we fundamentally changed the soap? Not much! We’ve just made it take up more space. If you try this experiment at home, you’ll find that the solid suds still work. Be sure to let your creation cool for a few minutes before you touch it.
We would like to thank you for visiting our blog. AstroCamp is a hands-on physical science program with an emphasis on astronomy and space exploration. Our classes and activities are designed to inspire students toward future success in their academic and personal pursuits. This blog is intended to provide you with up-to-date news and information about our camp programs, as well as current science and astronomical happenings. This blog has been created by our staff who have at least a Bachelors Degree in Physics or Astronomy, however it is not uncommon for them to have a Masters Degree or PhD. We encourage you to also follow us on Facebook, Instagram, Google+, Twitter, and Vine to see even more of our interesting science, space and astronomy information. Feel free to leave comments, questions, or share our blog with others. Please visit www.astrocampschool.org for additional information. Happy Reading!