A 0.03 mol sample of NH4NO3(s) is placed in a 1 L evacuated flask, which is then sealed and heated. The NH4NO3(s) decomposes completely according to the balanced equation above. The total pressure in the flask measured at 400 K is closest to which of the following?

Question

A 0.03 mol sample of NH4NO3(s) is placed in a 1 L evacuated flask, which is then sealed and heated.  The NH4NO3(s) decomposes completely according to the balanced equation above. The total pressure in the flask measured at 400 K is closest to which of the following?

Patricia · Accepted Answer

This was an multiple choice question on the 1999 AP Chem exam. The equation given on the exam was NH4NO3(s) --> N2O(g) + 2 H2O(g). Using this equation, the answer calculates to 2.95 atm, or 3 atm as an approximate answer when calculators are not permitted.

bobpursley · Answer

This sounds rather dangerous to me. Heating in a closed flask ammonium nitrate.

2NH4NO3 >> 2N2 + 4H2 + 3O2 so .03 moles of ammonium nitrate give .03 moles N2, .06 moles of H2, and .045 moles of O2

P=nRT/V=(.135mol*.083atm/Kmole*400K)
=4.48 atm check my work. Yes, it was dangerous. And, of course, one now has hydrogen and oxygen together as a gas in a closed hot system.

clarke · Answer

3 atm