# chem help, plz?

Sorry for a long question, but i just cant seem to figure it out.

The inflation mechanism of some automobile airbags contains a solid mixture of sodium azide, NaN3(s), potassium nitrate, KNO3(s) and silicon dioxide, SiO2(s). The chemical processes that occur during inflation of the airbag are described as follows. An electrical discharge initiates the decomposition of NaN3 into sodium, Na(s) and nitrogen, N2(g). Because Na is very reactive, KNO3is present to react with Na to yield K2O(s), Na2O(s) and some additional N2. Because K2O and Na2O are also very reactive, SiO2 is present to react with K2O and Na2O to yield K2O3Si(s) and Na2O3Si(s), respectively (both of which not reactive and nontoxic). The N2 generated in two of the reactions described above is what inflates the airbag.

a)Write down complete and balanced chemical equations for the four reactions described above.

b)The four reactions that you have written down in part a) are consecutive; combine the four reactions in such a way that you obtain a single balanced chemical equation that does not contain any of Na, K2O and Na2O in the reactant and product side of the equation.

c)If 100 g of NaN3 is required to inflate a particular air bag, determine the masses (in grams) of KNO3 and SiO2 required so that all of the Na, Na2O and K2O produced are completely eliminated.

d)What is the maximum size of airbag (in litres) that can be inflated using 100 g of NaN3 at 25.0 °C and 101 kPa?

### 1 Answer

- Roger the MoleLv 712 months agoFavorite Answer
a)

2 NaN3(s) → 2 Na(s) + 3 N2(g)

2 KNO3(s) + 10 Na(s) → K2O(s) + 5 Na2O(s) + N2(g)

SiO2(s) + K2O(s) → K2O3Si(s)

SiO2(s) + Na2O(s) → Na2O3Si(s)

b) Multiply the first and last equations by 5:

10 NaN3(s) → 10 Na(s) + 15 N2(g)

2 KNO3(s) + 10 Na(s) → K2O(s) + 5 Na2O(s) + N2(g)

SiO2(s) + K2O(s) → K2O3Si(s)

5 SiO2(s) + 5 Na2O(s) → 5 Na2O3Si(s)

Add all four equations:

10 NaN3(s) + 2 KNO3(s) + 10 Na(s) + SiO2(s) + K2O(s) + 5 SiO2(s) + 5 Na2O(s) →

10 Na(s) + 15 N2(g) + K2O(s) + 5 Na2O(s) + N2(g) + K2O3Si(s) + 5 Na2O3Si(s)

Cancel like amounts on opposite sides of the arrow:

10 NaN3(s) + 2 KNO3(s) + SiO2(s) + 5 SiO2(s) → 15 N2(g) + N2(g) + K2O3Si(s) + 5 Na2O3Si(s)

Combine like amounts on the same side of the arrow:

10 NaN3(s) + 2 KNO3(s) + 6 SiO2(s) → 16 N2(g) + K2O3Si(s) + 5 Na2O3Si(s)

c)

(100 g NaN3) / (65.00987 g NaN3/mol) = 1.53823 mol NaN3

(1.53823 mol NaN3) x (2 mol KNO3 / 10 mol NaN3) x (101.10332 g KNO3/mol) = 31.1 g KNO3

(1.53823 mol NaN3) x (6 mol SiO2 / 10 mol NaN3) x (60.0843 g SiO2/mol) = 55.5 g SiO2

d)

V = nRT / P = (1.53823 mol NaN3) x (8.3144626 L kPa/K mol) x (25.0 + 273.15) K / (101 kPa) =

37.8 L

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