system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does something like cocoa powder dissolve in hot liquids but not cold liquids?
gpt
When liquids are hot their molecules are moving around a lot because of the heat energy. When liquids are cold they're sluggish and slow.

The hot liquid molecules move around, constantly shifting, making room for other stuff to be stirred in and mixed. Cold liquid molecules don't move out of the way to make room for more stuff. 

Suppose you had a box of Raisin Bran cereal, but you wanted to add Lucky Charms to it. If you pour the Lucky Charms on top of the Raisin Bran and shake the box a little it'll mix a little(cold liquid, not much movement in molecules because low energy) If you shake the box vigorously it'll mix much better (hot liquid, lots of molecular movement because high energy). 

Hope this helps!