In some aquatic ecosystems, nitrate (NO_3^-) is converted to nitrite (NO_2^-), w

Question

In some aquatic ecosystems, nitrate (NO_3^-) is converted to nitrite (NO_2^-), which then decomposes to nitrogen and water. As an example of this second reaction, consider the decomposition of ammonium nitrite: NH_4NO_2(aq) rightarrow N_2(g) + 2 H_2O(l) What would be the change in pressure in a sealed 10.0 L vessel due to the formation of N_2 gas when the ammonium nitrite in 2.50 L of 1.490 M NH_4NO_2 decomposes at 25 degree C? PV = nRT Watch your units. The units of R will inform you as to what the units of every other variable need to be. The volume available to the gas is only the volume that isn't already occupied by liquids.

Explanation / Answer

Amount of NH4NO2 in 2.50 L solution = 1.490 moles * 2.50 L/1 L = 3.725 moles

This amount of solute (NH4NO2) will dissociate completely to form 3.725 moles of N2 and (2*3.725) or 7.45 moles of water.

volume of 55.55 moles of water = 1 L

so, volume of 7.45 moles of water = 7.45/55.55 L = 0.134 L

Total volume of liquid = 2.50 L solvent + 0.134 L water = 2.634 L

Volume occupied by N2 gas = 10 L - 2.634 L = 7.366 L

P = nRT/V

= 3.725 moles * 0.082 L.atm.mol-1.K-1 * 298 K/7.366 L

= 12.36 atm

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