Answer to Question #104232 in General Chemistry for Lauren Barad

Question

The chemical reaction that must happen for an airbag to go off happens in 3 stages following the series below.
1. 2NaN2 --> 2Na + 3N2
2. 10Na + 2KNO3--> 5Na2O + K2O+ N2
3. K2O + Na2O + SiO2 --> Glass.

Given the series above, answer the following questions
a. if 80g NaN3 reacts in reaction 1, how many grams of Na are produced?
b. What volume of N2 is produced by reaction 1 if 80 g NaN3 is used at STP?
c. As the only source of Na is the first reaction, based on your answer to 1b, how many liters of N2 are produced form reaction 2 at STP?
d. How many total liters of N2 are produced from this series of reactions at STP?
e. Lab tests with a particular airbag shows the airbag with a volume of 54.5L, what is the percent yield of this reaction? What real world conditions could be causing this difference?

Answer 1

a.From this reaction:  2NaN3 --> 2Na + 3N2 ,

a proportion can be made:

80/(2*65)=x/(2*23) ;

Where x - mass of Na produced;

23 - molar mass of Na;

80 - mass of NaN3;

65 - molar mass of NaN3;

2 - stoichiometric values of NaN3 and Na in this reaction;

Answer: m(Na)=28.3g;

b. 80/(2*65)=y/22.4*3;

y - volume of N2 in the first reaction;

y=41.35

Answer: V₁(N2)=41.35 liters;

c. 28.3/(23*10)=z/22.4 ;

z - volume of N2 in the second reaction;

z= 2.76;

Answer: V₂(N2)= 2.76 liters;

d. V_total(N2)= V₁(N2) + V₂(N2) = 2.76 + 41.35 = 44.11 liters;

e. φ=54.5/44.11=1.235= 123.5%. In real world condition the temperature and pressure can be different than stp (273 K; 1 atm). This is the main reason of the differense, because when temperature is higher (293-298 K) and pressure is lower, the volume of prodused gas will be higher.