Question
P9. (Sec. 12.4) The decomposition of cyclopropane is a first order reaction. At a temperature of 500 °C the rate constant (k) equals 6.11 x 10" s. If the initial concentration of cyclopropane, C3H6, is 0.226 M, what is the molar concentration of C3Hs after 20.5 minutes? a) 8.10 molVL b) 0.595 moV/L c) 0.106 mol/L d) 0.423 mol/L e) 0.0035 mol/L P10. (Sec. 12.4) A certain reaction A Products is a second order reaction. What is the value of the rate constant (k) if initially the concentration of A was 1.55 M and after 85 minutes the concentration of A measured 0.455 M? a) 0.0183 M min b) 0.0686 M1 min c) 0.118 M min d) 0.251 M min e) 1.17 M min P11. (Sec. 12.4) A certain reaction A >Products is a first order reaction. What is the value of the rate constant (k) if initially the concentration of A was 0.855 M and after 50 minutes the concentration of A measured 0.545 M? What is the half-life of this reaction'? P11. (Sec. 12.4) A certain reaction A Products is afirst order reaction. What is the value of a) 0.00901 min1; 76.9 minutes b) 0.0832 min1; 8.32 minutes c) 0.0108 min1; 64.2 minutes d) 0.112 min1; 6.18 minutes e) 0.00901 min; 223 minutes
Explanation / Answer
p9)
Given:
[cyclopropane]o = 0.226 mol/L
t = 20.5 minutes = 20.5*60 s = 1230 s
use integrated rate law for 1st order reaction
ln[cyclopropane] = ln[cyclopropane]o - k*t
ln[cyclopropane] = ln(0.226) - 6.11*10^-4*1230
ln[cyclopropane] = -1.487 - 6.11*10^-4*1230
ln[cyclopropane] = -2.239
[cyclopropane] = 0.106 mol/L
Answer: c
p10)
use integrated rate law for 2nd order reaction
1/[A] = 1/[A]o + k*t
1/(0.455) = 1/(1.55) + k*85
2.198 = 0.645 +k*85
k*85 = 1.553
k = 1.83*10^-2 M-1min-1
k = 0.0183 M-1min-1
Answer: a
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