Automakers are always investigatingalternative reactions for the generation of g

Question

Automakers are always investigatingalternative reactions for the generation of gas to inflate airbags,

in part because the sodium produced in thedecomposition of NaN3(see Problem 5.63) presentssafety

concerns. One system that has been consideredis the oxidation of graphite by strontium nitrate(Sr(NO3)2),

as shown in the equationbelow.

5 C(s) + 2 Sr(NO3)2(s) SrO(s) + 2N2(g) + 5CO2(g)

Suppose a system is being designed using thisreaction, and the goal is to generate enoughgas to inflatea

bag to 60 L and 1.3 atm at 20°C. What isthe minimum mass of graphite that should be used in thedesign

of this system.

Explanation / Answer

    5 C(s) + 2 Sr(NO3)2(s) SrO(s) + 2N2(g) + 5CO2(g)       According to ideal gas equation:       PV = nRT       1.3 atm x 60 L = n x 0.0821atm-L / mol-K x 293 K         number of moles ofgaseous mixture = 3.242 moles         From the balancedequation it is clear that 5 moles of Coal on combustionyields 7 moles of gaseous products          For 3.242 moles of gaseous product the number of molesof Coal required is 2.316 moles of Coal           The amount of the coal required is 2.316 mol x12 g / mol                                                                    = 27.793 g       According to ideal gas equation:       PV = nRT       1.3 atm x 60 L = n x 0.0821atm-L / mol-K x 293 K         number of moles ofgaseous mixture = 3.242 moles         From the balancedequation it is clear that 5 moles of Coal on combustionyields 7 moles of gaseous products          For 3.242 moles of gaseous product the number of molesof Coal required is 2.316 moles of Coal           The amount of the coal required is 2.316 mol x12 g / mol                                                                    = 27.793 g

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