at 25 deg. C, the second-order reaction NOCl(g)NO(g)+
1/2 CL2(g) is 50% complete after 5.82 hours when the
initialconcentration of NOCl is 4.46 mol/l. how long will it
takefor the reaction to be 75% complete?

Respuesta :

Answer:

It will take 17.46 hours for the reaction to be 75% complete.

Explanation:

Half life for second order kinetics is given by:

[tex]t_{\frac{1}{2}=\frac{1}{k\times a_o}[/tex]

[tex]t_{\frac{1}{2}[/tex] = half life = 5.82 hour

k = rate constant =?

[tex]a_o[/tex] = initial concentration = 4.46 mol/L

[tex]5.82 hour=\frac{1}{k\times 4.46 mol/L}[/tex]

[tex]k=\frac{1}{5.82 hour\times 4.46 mol/L}=0.03852 L/mol hour[/tex]

Integrated rate law for second order kinetics is given by:

[tex]\frac{1}{[a]}=kt+\frac{1}{[a_o]}[/tex]

[a] = concentration left after time t = [tex]100\%-75\%=25\% of [a_o]=0.25[a_o][/tex]

[tex]\frac{1}{0.25\times 4.46 mol/L}=\frac{1}{0.03852 L/mol hour}\times t+\frac{1}{4.46 mol/L}[/tex]

[tex]t=17.46 hours[/tex]

It will take 17.46 hours for the reaction to be 75% complete.

It will take 17.7 hours for the reaction to be 75% complete.

From the question, we can see that;

Half life of the reaction = 5.82 hours

Initial concentration of NOCl =  4.46 mol/l

Half life of a second order reaction is given by;

t1/2 = 1/k[A]o

k = 1/t1/2[A]o

k = 1/5.82 × 4.46

k = 0.038 Mol-1 L hour-1

When the reaction is 75% complete, the amount of  NOCl = 100 - 75 = 25%

[A]t = 0.25 × 4.46 mol/l = 1.115 mol/l

For a second order reaction;

1/[A]t = kt + 1/[A]o

1/[A]t - 1/[A]o = kt

Substituting values;

(1.115)^ -1 - (4.46)^-1 =  0.038t

0.897 - 0.224/ 0.038 = t

t = 17.7 hours

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