Phase Change Demonstrations | Chemistry Matters

This segment of the video script features a classroom demonstration centered around the properties and effects of liquid nitrogen. The host introduces a special guest, Adrian Elliot from Atlanta's Fernbank Science Center, to conduct a series of experiments. Adrian explains that nitrogen, the most abundant gas in the atmosphere, can be cooled to its condensation point of -196 degrees Celsius to become liquid nitrogen, which boils at room temperature. The demonstration showcases the phase change of condensation, where liquid nitrogen is poured into a metal bowl with warm water, causing water vapor in the air to condense into small droplets, forming a visible white cloud. Further, Adrian demonstrates the phase changes by placing a banana and a flower into the liquid nitrogen, highlighting the rapid freezing and brittleness that results. The banana, once removed, shatters due to the quick freezing of its internal water, while the flower undergoes a similar transformation. The segment concludes with a discussion on the long-term effects of such rapid freezing on the cellular structure of the banana.

In this part of the script, Adrian continues the demonstration by exploring the effects of liquid nitrogen on balloons filled with different gases. Initially, he uses an orange balloon filled with air to illustrate how the kinetic energy of gas particles gives the balloon its shape. After submerging the balloon in liquid nitrogen, the gas particles slow down, causing the balloon to deflate. Upon removal, the balloon gradually reinflates as the gas particles regain their kinetic energy. Adrian then uses a 'puppy' balloon to further demonstrate the phase changes from gas to liquid and solid, and back to gas, emphasizing the impact of atmospheric pressure. Finally, he experiments with helium balloons, showing that cooling the gas inside causes the balloons to lose their buoyancy temporarily, but they regain it once returned to room temperature. This segment highlights the relationship between temperature, gas particle energy, and pressure.

Adrian and the host delve into the concept of intermolecular forces and their role in phase changes. Using water and liquid nitrogen as examples, Adrian explains the differences in their intermolecular forces—hydrogen bonds in water and dipole-dipole interactions in nitrogen—and how these forces affect their boiling points. The segment also touches on the concept of sublimation, a phase change where a solid turns directly into a gas without becoming a liquid. The host and Adrian conduct a final experiment with a racket ball submerged in liquid nitrogen, which becomes extremely brittle and shatters upon being struck with a hammer, visually demonstrating the impact of phase changes on the physical properties of objects.

The final part of the script transitions to a classroom setting where the professor and students discuss sublimation and deposition, two less common phase changes. The professor introduces dry ice as an example of sublimation, where solid carbon dioxide turns directly into gas at -78.5 degrees Celsius. The students observe the sublimation process as dry ice is placed in water, creating a fog. The discussion then moves to iodine, another substance that can sublimate, and the students witness the direct transition from solid to gas and back during a controlled experiment. The professor also connects these concepts to natural phenomena like snowflake formation and the comet tails seen in space, emphasizing the relevance of these phase changes beyond the laboratory. The segment concludes with a review of the major phases of matter and the different phase transitions covered in the video, encouraging further exploration of these concepts.