In a collision of sufficient force, automobile air bags respond by electrically triggering the explosive decomposition of sodium azide (NaN3) to its elements. A 29.4−g sample of sodium azide was...

Question

decomposed, and the nitrogen gas generated was collected over water at 26°C. The total pressure was 733.8 mmHg. How many liters of dry N2 were generated?

Answer 1

Hi Dawson H.,

First, write the balanced equation for the NaN₃ decomposition. It decomposes to Na (metal, which rapidly reacts with air) and N₂ gas.

Next, determine (add up from the Periodic Table, or look up) the molar mass of each material.

3) Convert the mass of NaN₃ into moles.

4) Carry that value in moles across to N₂ gas product, using the ratio of the coefficients of the materials in the balanced equation.

5) Look up the vapor pressure of water at 26C. Subtract that from the given pressure of final gas, to calculate the partial pressure of just the N₂.

6) Using the Univeral Gas Law, find the V for that P, n, and T (R is also used, but that's a constant, not an experimental datum). Now ratio up from the partial pressure of the N₂, to the total measured pressure, since the water vapor also takes up space, but only proportional to its partial pressure.

That's it. There are alternate ways of calculating the same result on the gas mixture, but this one has the advantage that you are dealing with just the nitrogen, until the final volume ratioing up.

--C heers, -- Mr. d.