Question

Filling Air Bags Automobile air bags produce nitrogen gas from the reaction:


a. If 2.25 g of NaN3 reacts to fill an air bag, how much P–V work will the N2 do against an external pressure of 1.00 atm given that the density of nitrogen is 1.165 g/L at 20°C?


b. If the process releases 2.34 kJ of heat, what is ∆E for the system?

Answer 1

(a) The work done by the nitrogen against external pressure is 126.66 J.

(b) The change in the internal energy of the system is -2,466.66 J.

The given parameters:

• Mass of the compound, = 2.25 g
• External pressure, P = 1.0 atm = 101325 Pa
• Density of Nitrogen gas, ρ = 1.165 g/L
• Temperature of the Nitrogen gas, T = 20⁰C

The molar mass of the given compound is calculated as follows;

NaN₃ = 23+ (14 x 3) = 65 g/mol

65 g -------------- 42

2.25 g ------------- ?

$= \frac{2.25 \times 42}{65} \\\\= 1.45 \ g$

The volume of the nitrogen gas is calculated as follows;

$\rho = \frac{m}{V} \\\\V = \frac{m}{\rho} \\\\V = \frac{1.45}{1.165} \\\\V = 1.25 \ L$

$V = 0.00125 \ m^3$

The work done by the nitrogen against external pressure is calculated as follows;

$W = PV\\\\W = 101325 \times 0.00125\\\\W = 126.66 \ J$

The change in the internal energy of the system is calculated by applying first law of thermodynamics as follows;

$\Delta E = Q - W\\\\\Delta E = (-2,340) - (126.66)\\\\\Delta E = -2,466.66 \ J$

Learn more about first law of thermodynamics here: https://brainly.com/question/2965070