Most substances melt when heated so why do eggs turn from liquid to solid (scrambled egg) as I cook it?
Raw eggs are already liquid at room temperature. If you froze them, then they would melt when you heated them. They solidify when you heat them up above room temperature, in the same way that anything containing protein does (I won't go into examples on this one), because the protein coagulates, due to minor changes in the chemical structure.
If you heated the cooked eggs even hotter, they would burn, but if you did it in a high pressure inert environment, like a pressure vessel filled with argon, the cooked eggs would again liquefy. Of course, when you cooled them down again, they would set, but you could I guess put the molten egg in some eggshell molds, and then when it set it would be egg-shaped again.
Why does a bicuit left out overnight go soft but a slice of bread left out overnight go hard?
biscuits and bread left out over night can turn both soft OR hard, depending on...dunno.
i do know however, that buscuits (~200 years ago, on sea) would turn hard as bricks...while these days they turn soft...:S
same goes for bread.
i suppose that it has something to do with the amount of liquid stored in them but i really dont have a clue
If biscuits were left for 200 years in the sea, surely they would turn soft? Not hard as bricks?
But yes - I believe this one is a water related point. Biscuits absorb water becaue they are very dry. When they do, they go soft. Bread has quite a lot of water in (hence you can freeze it). This comes out when you leave it, and it goes dry.
It's all about achieving equilibrium with the atmosphere - if the amount of water in the food is greater concentration than in the atmosphere, the food loses water to the atmosphere. An extreme example is a puddle which dries out on a dry sunny day. If the food has less water than the atmosphere, it will absorb water. An extreme example here is washing powder, which will absorb water and go lumpy.
Damn i miss physics