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1) (24 pts) Automotive air bags inflate when sodium azide, NaN3, rapidly decomposes to its component elements upon ignition with an electrical spark

Chemistry

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1) (24 pts) Automotive air bags inflate when sodium azide, NaN3, rapidly decomposes to its component elements upon ignition with an electrical spark.Hint: Remember to balance the equation!

NaN₃ (s)  ^___________>       Na(s)   +       N₂ (g)

(a) How many moles are there in 10.0 g of NaN₃?

                                             ____0.153___mol NaN₃ 

       10.0g x 1mol/65.0099 = 0.1538

    (this is what I got but I'm not sure if it's right)

 (b) How many grams of nitrogen gas (N₂) can you produce from the amount of 

        NaN₃ given in (a)?

                                                      _______ g N₂

   (c) A typical air bag is designed to contain 65 L of nitrogen gas (N₂), which has a 

       density of 1.25 g/L. How many moles of nitrogen gas do you need to produce? Hint: Use the density formula to solve for grams (from the volume), and then find the number of moles from the molar mass of N₂.

                                                      __________ moles N₂

   (d) Is the amount of NaN₃ from (a) enough for a typical air bag, as in (c)?  Explain your choice, briefly.  

                                                                Yes  No 

2)(10 pts ) A piece of copper metal has a mass of 6.22 grams. Its specific heat is 

   0.385J/g ^oC. Calculate the amount of heat needed to take it from 20.5 ^oC to 324.3 ^oC.

  [See p. 2, lecture notes, CH. 7]                                 ________ J       

2) (15 pts) The first step in the preparation of lead from its ore (galena, PbS) consists of "roasting" the ore in the following way:  

 

             ____PbS (s)    +   ___ O₂ (g)  ^______>  ___SO₂ (g)  + ____PbO(s)

ΔH_f (g/mol)       (-98.32)            (0)             (-296.8)       (-219.0)

(a) Balance the equation. 

(b) Calculate the standard enthalpy change for this reaction, using enthalpies of formation (values are given below each substance) [See p. 7, lecture notes for an example (Ch. 7).] 

                                               _____________ kJ, ΔH_f