3. (20 pts) Airbags in automobiles contain 60.0 g NaN3(s) that, upon sudden dece

Question

3. (20 pts) Airbags in automobiles contain 60.0 g NaN3(s) that, upon sudden deceleration (i.e. impact!), is electrically detonated, resulting in the following instantaneous reaction: NaN3(s) N2(g) Na(s) + The nitrogen gas (assumed to be ideal) formed by the reaction expands against a constant external pressure of 1.00 atm to fill the bag. (Neglect the volume of the solids and further reactions of the Na.) The temperature of the interior of the car is 20.0°C and the expansion of the N2(g) occurs rapidly, but not adiabatically, to its final volume, where the N2() in the bag is-50°C. Determine waqdhEand H for the inflation of the airbag.

Explanation / Answer

this is an example of irreversible expansion

let us find the final volume first (initial vol is 0)

moles of nitrogen =moles of sodium azide since all of it detonates into nitrogen and sodium

moles of NaN3 = 60/ 65= 0.92= moles of N2

T= -15oC = 258K

PV=nRT (since N2 is considered ideal gas)

1*V= 0.92 * 0.082 * 258

Vf= 19.46 L

w= -PextdelV

= -101325* (0.01946-0)

w= -1972J

q= nCpdelT

= 0.92* 4* 8.314* (258-293)

q = -1070 J

delE = q + w

=-1070 + (-1972)

delE= -3042 J

delH = delE + pdelV

= -3042 + 101325 (-0.0196)

delH = -5026 J

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