Molecular iodine, I2(g), dissociates into iodine atoms at 625 K with a first-order rate constant of 0.271 s−1.
(a) What is the half-life for this reaction?
(b) If you start with 0.052 M I2 at this temperature, how much will remain after 5.16 s assuming that the iodine atoms do not recombine to form I2?

Respuesta :

Answer:

a) Half life = 2.56 s

b) Remaining concentration after 5.16 s = 0.0128 M

Explanation:

Given,

Rate constant = [tex]0.271\;s^-1[/tex]

a)

Half life of a first order reaction is given by,

Half life = [tex]\frac{ln2}{rate\;constant}[/tex]

             = [tex]\frac{ln2}{0.271} =2.56s[/tex]

b)

Integrated rate law for first order reaction is:

                         [tex]A = A_0\times exp(-kt)[/tex]

Where,

A = Concetration after time 't'

A0 = Initial concentration = 0.052 M

k = rate constant = 0.271 s^-1

t = time = 5.16 s

[tex]A = A_0\times exp(-kt)[/tex]

[tex]A = 0.52\times exp(-0.271 \times 5.16)\\\; \; \; \; \; =0.0128\;M[/tex]

a) Half life = 2.56 s

b) Remaining concentration after 5.16 s = 0.0128 M

Half life for first order reaction:

The half-life of a first-order reaction is a constant that is related to the rate constant for the reaction:

[tex]t_{1/2}=\frac{0.693}{k}[/tex]

Given:

Rate constant = [tex]0.271 s^{-1}[/tex]

a)

[tex]\text{Half life} =\frac{0.693}{k}\\\\ t_{1/2}= \frac{0.693}{0.271}\\\\ t_{1/2}= 2.56s[/tex]

b)

Rate law for first order reaction is given by:

[tex]A=A_0*exp(-kt)[/tex]

where,

A = Concentration after time 't'

A₀ = Initial concentration = 0.052 M

k = rate constant =  [tex]0.271 s^{-1}[/tex]

t = time = 5.16 s

On substituting the values:

[tex]A=A_0*exp(-kt)\\\\A=0.52*exp(0.271*5.16)\\\\A=0.0128M[/tex]

Thus, the concentration that will remain after will be 0.0128M.

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