Advertisements
Advertisements
Question
What is half life of first order reaction if time required to decrease concentration of reactants from 0.8 M to 0.2 M is 12 hours?
Advertisements
Solution 1
Given: [A]0 = 0.8 M, [A]t = 0.2 M, t = 12 hours
To find: Half life of reaction (t1/2)
Formulae:
- k = `2.303/"t" log_10 (["A"]_0)/(["A"]_"t")`
- `"t"_(1/2) = 0.693/"k"`
Calculation: Substituting given value in
k = `2.303/"t" log_10 (["A"]_0)/(["A"]_"t")`
k = `2.303/(12 "hr") log_10 0.8/0.2`
= `2.303/(12 "hr") log_10 (4)`
= `2.303/(12 "hr") xx 0.6020`
= Antilog10 (log10 2.303 + log10 0.6020 − log10 12)
= Antilog10 (0.3623 + `bar(1).7796` − 1.0792 )
= Antilog10 `(bar(1).0627 )`
= 0.1115 hr–1
`"t"_(1/2) = 0.693/"k" = 0.693/(0.1155 "hr"^-1)` = 6 hr
Solution 2
Concentration is reduced to 25%. It means it takes two half-lives to decrease the concentration of reactant from 0.8 M to 0.2 M in first-order reaction. Hence, half-life of the reaction is 12/2 = 6 hours.
The half life of reaction is 6 hours.
APPEARS IN
RELATED QUESTIONS
Answer the following in one or two sentences.
Write the relationships between rate constant and half-life of the first order and zeroth-order reactions.
What are pseudo-first-order reactions?
How will you represent first order reactions graphically.
In a first-order reaction, the concentration of the reactant decreases from 20 mmol dm−3 to 8 mmol dm−3 in 38 minutes. What is the half-life of reaction?
Solve
The half-life of a first-order reaction is 1.7 hours. How long will it take for 20% of the reactant to react?
Answer the following in brief.
What are the units of the rate constant?
Derive the integrated rate law for the zeroth order reaction.
Rate constant of a reaction is 3.6 × 10–3 s–1. The order of reaction is ______.
Write a mathematical expression for integrated rate law for zero-order reaction.
For a first-order reaction \[\ce{A -> B}\] the rate constant is x min−1. If the initial concentration of A is 0.01 M, the concentration of A after one hour is given by the expression.
This reaction follows first-order kinetics. The rate constant at particular temperature is 2.303 × 10−2 hour−1. The initial concentration of cyclopropane is 0.25 M. What will be the concentration of cyclopropane after 1806 minutes? (log 2 = 0.3010)
For a first-order reaction, the rate constant is 6.909 min−1 the time taken for 75% conversion in minutes is
Describe the graphical representation of first order reaction.
The time of completion of 90% of a first order reaction is approximately ____________.
If [A]0 is the initial concentration, then the half life of zero order reaction is ____________.
The activation energy of a reaction is zero. Its rate constant at 280 K is 1.6 × 10-6 s-1, the rate constant at 300 K is ______.
The rate constant of a first order reaction is 3 × 10−6 per s. If the initial concentration is 0.10 mol dm−3, the initial rate of reaction is ____________.
In a first order reaction, the concentration of the reactant is reduced to 25% in one hour. The half-life period of the reaction is ____________.
The rate of formation of B at time t for reaction \[\ce{2A -> 3B}\] is equal to ____________.
For a first order reaction, \[\ce{A -> B}\], if [A] = 1 M and rate is 4 × 10−2 M s−1. What is the rate constant of the reaction?
The integrated rate equation is Rt = log C0 – log Ct, then the straight-line graph is obtained by plotting.
If the rate constant for a first-order reaction is k, the time (t) required for the completion of 99% of the reaction is given by:
The rate constant for a first order reaction is 7.0 × 10-4 s-1. If initial concentration of reactant is 0.080 M, what is the half-life of reaction?
Which is the relation between half life and rate constant for a zero order?
A radioactive isotope decayed to 17/32 of its original mass after 60 minutes. Find the half-life of this radioisotope.
Which of the following correctly represents integrated rate law equation for a first order reaction in a gas phase?
A first order reaction takes 10 minute for 30% completion. Find rate constant of the reaction.
