Airbag Stoichiometry
Part 1
1. Open the Excel file “Airbags and Stoichiometry.” There are two sheets on this file: the Stoichiometry
sheet and the Gas Laws sheet. Make sure that you are on the Stoichiometry sheet.
2. Write the balanced chemical equation for the decomposition of sodium azide, NaN3.
3. What value is controlled by the slider bar?
4. Use the slider bar to pick any starting mass for the sodium azide (NaN3) and record that mass. ________
5. Observe the masses of the products in the excel sheet. Show the work required to arrive at those
answers.
To find mass of Na:
To find mass of N2:
6. Click on cell D6. Copy the formula in the formula bar. It should look very similar to your work for finding
the mass of Na in step 5.
7. Predict the formula in the formula bar for cell F6 (mass of N2).
8. Check your formula in the Excel worksheet by clicking on cell F6. Are they the same? If not, ask for
help.
9. Show the work necessary to determine the number of moles of nitrogen gas produced.
10. Write a formula in cell H6 to determine the number of moles of nitrogen gas produced. Does the
number in cell H6 agree with your answer above? If not, ask for help.
Part 2
Click on the “Gas Laws” tab of the excel worksheet. Notice that the data for moles of N2 comes from cell H6 on
the Stoichiometry sheet. The gas laws sheet uses the moles of N2 calculated on the Stoichiometry sheet to
calculate the volume of an airbag with a given set of conditions.
1. Manipulate the pressure and temperature sliders and observe their effect on the final volume.
a. Choose a certain pressure and record the volume at that pressure. Double the pressure and
record the new volume. What happens to the final volume when you double the pressure?
b. Choose a certain temperature and record the volume at that temperature. Double the
temperature and record the new volume. What happens to the final volume when you double
the temperature?
c. What happens to the final volume when you double the number of moles of N2? (This one is
tricky because you will have to use the slider bar to manipulate the mass of NaN3 on the
stoichiometry sheet to change the moles of N2 on this sheet.)
2. Complete the table below by filling in the cell location of the value that correlates to each variable. The
first one has been done for you as an example.
Variable
P
Cell Location
E6
V
n
R
T
3. Write the formula for the gas law in Excel form using the cell locations above.
4. Which cell has the formula, in Excel form, for the ideal gas law in the formula bar? (Hint: It may be a
variation of your formula but the cells will correlate to all the variables in the gas law.)
Part 3
The decomposition of the NaN3 is only one of the reactions that occur in an airbag. You can see that one of the
products of the reaction is elemental sodium, which we know to be dangerous. The sodium can be removed by
a second reaction with potassium nitrate, KNO3, in the following, unbalanced chemical equation.
Na + KNO3  Na2O + K2O + N2
1. Balance the chemical equation for the reaction of sodium with potassium nitrate and write it below.
2. Nitrogen gas, the gas responsible for inflating the air bag is also produced in this second reaction. You
need to add this reaction to the Excel model to determine the total volume of nitrogen gas produced.
3. Based on your model of the first reaction, make a second Excel model to determine the amount of
nitrogen gas produced from this second reaction. Keep in mind the following points:
a. It may be easiest to input your reaction below the first reaction on the Stoichiometry sheet.
b. The amount of Na you start with should be the same as the Na produced in the first reaction, so
that cell should be equal to cell D6 on the Stoichiometry sheet.
c. Make sure you create a cell that calculates the number of moles of N2 gas created in this
reaction. Show the work necessary to determine the moles of nitrogen gas produced in the
second reaction.
4. Your ultimate goal is to determine the total number of moles of nitrogen produced from both
reactions. This can be done by adding the cell containing the moles of N2 from the second reaction to
the number of moles produced in the first reaction which is in cell A6 on the gas laws sheet. Write the
Excel formula for the total number of moles produced in cell A12 on the “gas laws” sheet.
5. Once you have built your model, decide on a starting amount of NaN3. Show the work necessary to find
the total volume of Nitrogen gas, N2, produced at STP. See if that number agrees with the value
produced by the model in cell B12. If not, ask for help
6. Use the Ideal Gas Law to calculate the volume of nitrogen gas, N2 that would be produced at the current
temperature and pressure of the room. Set the slider bars for these values of temperature and pressure
on the “gas laws” sheet and see if the volume in cell G6 agrees with the volume you calculated.
7. If your numbers agree, have the instructor sign this sheet to verify he or she has looked over your work
to make sure it is accurate.
__________________________________________(teacher signature)