Question

1. Suppose we fill a sealed flask with 0.250 mol of gas A, which then completely reacts to form a second gas, B, according to the reaction: A → 2B. At various times during the reaction, we measure the amount of B in the flask and get the following data:

Time (s)	0.00	30.0	60.0	90.0	120
Moles of B	0.000	0.167	0.278	0.350	0.400

a. Calculate the number of moles of A remaining in the flask at each time in the table.

b. Calculate the average rate of disappearance of A for each interval in the table, in units of mol/s. (show work)

Answer 1

A = 2B

mol of A remaning

mol of A1 = Ainitial - 1/2*B = 0.25 - 1/2*0.00 = 0.25

mol of A2 = Ainitial - 1/2*B = 0.25 - 1/2*0.167= 0.1665

mol of A3 = Ainitial - 1/2*B = 0.25 - 1/2*0.278= 0.111

mol of A4 = Ainitial - 1/2*B = 0.25 - 1/2*0.35= 0.075

mol of A5 = Ainitial - 1/2*B = 0.25 - 1/2*0.40= 0.05

b)=

average rate of diss. of A in each interval

dC/dT = Ai+1 - Ai / (ti+1 - ti)

dC1/dT =(0.1665-0.25)/(30-0) = -0.002783 M/s

dC2/dT =(0.111 -0.1665)/(60-30) = -0.00185 M/s

dC3/dT =(0.075-0.111 )/(90-60) = -0.0012M/s

dC4/dT =(0.05 -0.075)/(120-90) = -0.00083333333M/s