حامد خان به متن زیر توجه کن.......گفتم که قابل بحثه آخه شماها دارید فقط phase diagram درنظر میگیرید در حالی که مساله اصلی rate انتقال حرارت هست.
Water boils when the vapor pressure equals atmospheric pressure at the water's surface. The vapor pressure increases with temperature. So you might reason that with a lid on, the pressure at the surface of the water would increase a bit, which would mean that you need higher temperature to get the vapor pressure up a bit higher. Getting the temp up a bit higher would take a bit longer, so using this line of reasoning you would expect the water to take longer to boil.
But that's wrong.
With no lid, you lose quite a bit of energy as the hot vapor evaporates from the surface and leaves the pot.You lose significantly less when you put a top on the pot. You don't stop the loss completely becasue the typical lid is a loose fit and not well-insulated, but a lid on the pot helps quite a bit anyway. With a lid, more of the the heat from your stove goes into raising the temperature (and thus the vapor pressure) of the water, and LESS is lost out the top, so it reaches the boiling point sooner.
Secondly, having a typical loose fitting lid on a pot doesn't really increase the pressure at the surface of the water to any significant degree. A pressure cooker or car radiator is another story because they're well sealed.
So yes, covering the pot will boil your water faster.
In a related fashion, if you have to leave your coffee for a few minute, put something over the top of the cup. Most of the heat loss is from the surface of the coffee (same as the pot of water). So if you retard the evaporative loss by putting something over the cup, it'll stay warmer quite a bit longer. A porcelain tile works quite well!
Now, sometimes you want your water to boil at a higher temperature to cook your food faster. Which is what you use a pressure cooker for. By sealing the vessel, the pressure increases and thus the boiling point goes up.
Your car radiator works the same way. Of course you should have antifreeze in there, which has a higher boiling point to start with. But the pressurization allows the system to run even hotter before you get a boil-over.
Another way to cook your pasta at a higher temperature is to salt the water a bit. When you add an impurity (the salt in this case) to water, the boiling point elevates and the freezing point depresses. Salted water will take a bit longer to boil than pure water, but it will be a few degrees hotter than pure water.