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6. The rxn C 2 H 6 (g) --> 2CH 3 (g) is a first order rxn. If k = 5.50*10 -4 s -

ID: 1041933 • Letter: 6

Question

6. The rxn C2H6(g) --> 2CH3(g) is a first order rxn. If k = 5.50*10-4s-1 and [C2H6] is initially 0.0200M, calcualte the final concentration after 1.25 hours.

7. What is the half-life, in seconds, if it takes a first order reactant 185 seconds to drop from 0.0420M to 0.0110M?

8. Concsider the following rxn:

N2(g) + O2(g) + heat <--> 2NO(g)

a. Will equilibrium shift to the right or left or remain constant if temperature is increased

b. Will the equilibriu shift to the right or to the left or remain constant when the pressure is decreased?

9. For the rxn below, identify if each stress will cause a shift to the right ot left?

CH4(g) + 2H2S(g) <--> CS2(g) + 4H2(g)

a. decrease the concentratio nof dihydrogen sulfide

b. increase the pressure on the system

c. decrease the concentration of hydrogen

d. increase the concentration of carbon disulfide

Explanation / Answer

6)

rate = k [C2H6]

time = 1.25 hr = 4500 sec

k = 1/t ln (Ao / At)

5.50 x 10-4 = 1/ 4500 ln (0.0200 / At)

At = 0.00168

concentration after = 0.00168 M

7)

k = 1/185 ln (0.0420 / 0.0110)

k = 7.24 x 10^-3 s-1

half - life = 0.693 / k

                = 0.693 / 7.24 x 10^-3

half - life = 95.7 sec

8.

N2(g) + O2(g) + heat <--> 2NO(g)

a ) equilibrium will shift to the right

b.) no shift .

Dr Jack
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