Ice has to absorb energy in order to melt, changing the phase of water from a solid to a liquid. When you use ice to cool the ingredients for ice cream, the energy is absorbed from the ingredients and from the outside environment. When you add salt to the ice, it lowers the freezing point of the ice, so even more energy has to be absorbed from the environment for the ice to melt. This makes the ice colder than it was before, which is how your ice cream freezes. Ideally, you would make your ice cream using 'ice cream salt', which is just salt sold as large crystals instead of the small crystals you see in table salt. The larger crystals take more time to dissolve in the water around the ice, which allows for even cooling of the ice cream.
Striking a match starts a chemical reaction. A safety match can only light when someone strikes it against the striking surface on the side of the match box. A "striking surface" is made of sand, powdered lass, and "red phosphorus". The head of a safety match is made of sulfur, glass powder, and an oxidizing agent. An oxidizing agent is a chemical that takes electrons from another chemical. When a chemical loses electrons we say it has been oxidized. An oxidizing agent is necessary to keep a flame lit. Oxygen gas is a common oxidizing agent.
When a match is struck on the striking surface of its box, the friction caused by the glass powder rubbing together produces enough heat to turn a very small amount of the red phosphorus into white phosphorus, which catches fire in air. This small amount of heat is enough to start a chemical reaction that uses the oxidizing agent to produce oxygen gas. The heat and oxygen gas then cause the sulfur to burst into flame, which then catches the wood of the match to catch on fire.
No comments:
Post a Comment