[zerobladex]

Hey guys, i got a question that i need help with and goes something like this:

If all the water vapor in the atmosphere were condensed into liquid water and the change in energy was captured, how much energy would this be assuming that the atmosphere is 2% water vapor in volume?

I have an idea of how to solve it but I'm hitting some bumps in the road.
First you could use the ideal gas law to calculate the number of mols and then you could just calculate the change in enthalpy by multiplying the number of mols by the heat of vaporization for water. The problem I'm getting is I dont know how to calculate the amount of mols.

Right now I'm assuming that P = 1 ATM and t = 273.15 K but I don't know what to do for V, so any suggestions are greatly appreciated.

[Borek]

Don't feel alone, I have no idea what to use for V as well. Try to google it, or check what data on atmosphere you will find in encyclopedias or wiki. Perhaps you will get mass from there.

[pear]

I Googled it as well, but then it dawned on me... the pressure of the atmosphere changes as you ascend, so I have no idea if you could even make the 1 atm assumption.

[Borek]

That's why I suggested starting with the mass...

[billnotgatez]

This WIKI page gives lots of data about the earth's atmosphere to include the approximate mass. Since it is a WIKI page you might confirm the data elsewhere (library)

http://en.wikipedia.org/wiki/Earth's_atmosphere

You might make the same no greater than assumption that is done when trying to determine how many grains of sand are in the earth. It can be no greater than if all the earth were sand. Since the upper atmosphere does not hold water but is a small portion of the atmosphere you ignore it and assume you are close enough.

Maybe this is not what your teacher wants but it is what I would do.

Note the WIKI article say the percent of water is about one in the atmosphere.

[billnotgatez]

Here are a few more interesting pages

http://www.theweatherprediction.com/habyhints/40/
http://scipp.ucsc.edu/outreach/balloon/atmos/The%20Earth.htm

[billnotgatez]

i got this information as well from google

There is always water in the atmosphere. Clouds are, of course, the most visible manifestation of atmospheric water, but even clear air contains water—water in particles that are too small to be seen. One estimate of the volume of water in the atmosphere at any one time is about 3,100 cubic miles (mi3) or 12,900 cubic kilometers (km3). That may sound like a lot, but it is only about 0.001 percent of the total Earth's water volume of about 332,500,000 mi3 (1,385,000,000 km3), as shown in the table below. If all of the water in the atmosphere rained down at once, it would only cover the ground to a depth of 2.5 centimeters, about 1 inch.
http://ga.water.usgs.gov/edu/watercycleatmosphere.html