[P4 Science - J1 Chemistry: Heat & reaction between oxygen & ethanol] You often know heat as a dangerous form of energy. The reason kids are often not allowed in the kitchen without supervision, of course, is because they rely on their eyes too much. They're not careful enough to catch onto the fact that heat is an energy, so it's not always visible.
As a result, a hot oven can't be distinguished just by looking inside the oven. Same deal with hot water - One usually has to hover their hand over it to catch hints of hot vapour leaving the liquid, but kids are too careless and reckless, they often pick up the cup without first testing its temperature and end up scalding themselves.
There are cases of invisible fires, though. Beware:
The conversion of ethanol to carbon dioxide and water is easy because of the chemical structure of the ethanol. It features a single bond with a hydroxide component (-O-H) as well as a double bond with oxygen (C=O). When burning oxygen, the molecular bonds between the oxygen are separated and bonded with the other atoms (mainly the hydrogen and hydroxide components) to reach a more stable state.
(since the id-id attraction between the hydrogen and oxygen is much higher than carbon, given the larger size of the electron cloud oxygen has which displaces the carbon for the much-stabler hydrogen- Ahh blargah-flargah-kids don't understand this.)
Basically, Hydrogen and Oxygen like reacting with each other more (due to reasons too complicated for kids and teens), and Carbon's left all alone like the worn-out pair of slippers at home. But, because carbon is in the presence of excess oxygen during the burning process, it gets attached to an oxygen molecule to make carbon dioxide.
As mentioned in the video, CO2 is a very clean and colourless gas. So the fire appears invisible. So, be careful when interacting with a naked flame - Your sanitiser-covered hands might just catch on fire if you aren't careful. Stay safe!