A sample of nitrogen gas is collected over water at 20°C. The vapor pressure of water at 20°C is 18 mmHg. What is the partial pressure of the nitrogen if the total pressure is 765 mmHg?

1 Answer
anor277
Jun 13, 2016

#P_"measured"=P_"SVP"+P_"Gas"#

Explanation:

#P_"SVP"# is the saturated vapour pressure, which is the vapour pressure of water, and is extensively tabulated across a range of temperatures. Of course, at #100# #""^@C# the saturated vapour pressure is #1# #atm#. Why?

So if we want #P_"Gas"# (which we do), all we have to do is subtract #P_"SVP"# from #P_"measured"#

#P_"measured"-P_"SVP"# #=# #P_"Gas"# #=# #(765-18)*mm*Hg#

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