Sir
Please guide me about why water vaporates in vaccum?
Sir
Please guide me about why water vaporates in vaccum?
In a vacuum, water evaporates like in dry air (this is why sweating cools you in dry hot weather). Evaporation is independent of any other gas molecules that happen to be around.
In humid air (100% humidity), there is an equilibrium between vapor and liquid. The equilibrium means that the same amount of molecules condensate per second as other ones evaporate, so that the net change is zero.
The evaporation rate is high if the temperature is high. A molecule evaporates from the liquid or solid if it happens to get a speed that can overcome the attraction forces to the neighboring molecules. This can happen because temperature is a measure of the average speed of the molecules, there are always a few that are fast enough to escape. At higher temperatures, this happens more often.
The condensation rate is high if the fast moving water molecules in the gas phase that encounter the liquid or solid have so little energy that they “stick” and do not bounce off. This is not only happening often if the temperature (and hence the average speed) is low, but also if the concentration of water molecules in the vapor is high (the “partial pressure” of water is high).
The balance of the two rates happens (at any temperature) when the partial pressure of water is equal to the so-called vapor pressure. At the balance, it looks like the water is no longer evaporating, but we now know better: molecules still evaporate, but others condensate at the same rate. In a vacuum, this equilibrium will never happen, because the molecules in the vapor are immediately “diluted” away. This will actually cause the water not only to evaporate in a vacuum, but even to boil: bubbles of vapor will form inside the bulk of the liquid.
In a vacuum, water evaporates like in dry air (this is why sweating cools you in dry hot weather). Evaporation is independent of any other gas molecules that happen to be around.
In humid air (100% humidity), there is an equilibrium between vapor and liquid. The equilibrium means that the same amount of molecules condensate per second as other ones evaporate, so that the net change is zero.
The evaporation rate is high if the temperature is high. A molecule evaporates from the liquid or solid if it happens to get a speed that can overcome the attraction forces to the neighboring molecules. This can happen because temperature is a measure of the average speed of the molecules, there are always a few that are fast enough to escape. At higher temperatures, this happens more often.
The condensation rate is high if the fast moving water molecules in the gas phase that encounter the liquid or solid have so little energy that they “stick” and do not bounce off. This is not only happening often if the temperature (and hence the average speed) is low, but also if the concentration of water molecules in the vapor is high (the “partial pressure” of water is high).
The balance of the two rates happens (at any temperature) when the partial pressure of water is equal to the so-called vapor pressure. At the balance, it looks like the water is no longer evaporating, but we now know better: molecules still evaporate, but others condensate at the same rate. In a vacuum, this equilibrium will never happen, because the molecules in the vapor are immediately “diluted” away. This will actually cause the water not only to evaporate in a vacuum, but even to boil: bubbles of vapor will form inside the bulk of the liquid.
