Question

What happens during each phase change in terms of kinetic energy, particle motion, and intermolecular forces of attraction??

Answer 1

When particles in a material increase in kinetic energy (KE) they break the intermolecular forces (IMFs) that hold adjacent molecules (or atoms) together weaken (and eventually break apart).
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Side note: KE is just the energy associated with motion of stuff, represented by \(KE=\dfrac{1}{2}mv^2\). Consider two objects with the same mass, the one moving faster than the other. The object moving faster has a larger energy associated with it's motion.

In everyday life, this would be analogous to having someone walk into you versus having someone RUN into you, which one hurts more?
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Think of water. At cold temps it's ice, when it gets warmer it's liquid and when it's over 100 Celsius it's a gas (steam). The chemical composition didn't change in any of these phase transitions, merely the average space between individual water molecules.



When it's solid, it's ice, the water molecules have low KE and the IMFs that hold them together are stronger - because they are moving less. When the molecules gain some KE (by increasing the ambient temperature) the IMFs are weaker; similarly when it's hotter, it becomes a gas and the IMFs are the weakest.

I hope you know what IMFs are.. if not, essentially, they're associative forces like london dispersion forces (induced dipoles) or hydrogen bonds (permanent dipoles) that create partial charges on opposite sides of molecules, these associate with their neighbours and basically makes them stick to each other - this would be analogous to having 2 bar magnets stick.