Careers360 Logo
NEET 2024 Countdown - How Many Days Left for NEET Exam 2024

Access premium articles, webinars, resources to make the best decisions for career, course, exams, scholarships, study abroad and much more with

Plan, Prepare & Make the Best Career Choices

First Order Reaction - Practice Questions & MCQ

Edited By admin | Updated on Sep 25, 2023 25:23 PM | #NEET

Quick Facts

  • First Order Reaction, Half Life of First Order Reaction, Graphs of First Order Kinetics are considered the most difficult concepts.

  • 74 Questions around this concept.

Solve by difficulty

t_{1/4}  can be taken as the time taken for the concentration of a reactant to drop to 3/4 of its initial value. If the rate constant for a first order reaction is k, the  t_{1/4}  can be written as

The rate equation for the reaction 2A+B\rightarrow C is found to be : rate =k\left [ A \right ]\left [ B \right ]. The correct statement in relation to this reaction is that the

The half-life period of a first order reaction is 15 minutes. The amount of substance left after one hour will be :

Units of the rate constant of first and zero-order reactions in terms of molarity M unit are respectively.

Select the reaction which is not follows the first order Kinetics:

 

Apply to Amrita Vishwa Vidyapeetham Allied & Life Science 2024

Begin a career in Medical and Allied Sciences. Admissions Open for

If we start a reaction from 100 mol, having the rate constant is \mathrm{0.0693 \mathrm{~min}^{-1}}. What will be the rate of the reaction offer 20 min.

 

Which of the following reactions is first order reaction

Amrita Vishwa Vidyapeetham Allied & Life Science 2024

Admissions Open for multiple allied and health sciences programs across 5 campuses | Ranked #7 in India by NIRF, NAAC A++ Accredited

NEET College Predictor

Know possible Govt/Private MBBS/BDS Colleges based on your NEET rank

Which of the following correctly represents the first order reaction.

Which expression is not correctly represent the first order reaction?

Most Scoring Concepts in NEET(Latest NTA Syllabus)
Know Most Scoring Concepts in NEET 2024 Based on Previous Year Analysis
Know More

Consider a reaction \mathrm{A \rightarrow B+C} follow the first order kinetics with rate constant \mathrm{( k ) \: 0.02 \mathrm{~s}^{-1}}. What percentage of A will be left after after 5 half-lives?

Concepts Covered - 4

First Order Reaction

The rate of the reaction is proportional to the first power.

                                

The chemical reaction occurs as follows:

R    \rightarrow        P

a                 0

a-x             x

We have,
rate[r]=K[R]^{1}

\frac{-d(a-x)}{dt}=K(a-x)

\frac{-dx}{dt}=K(a-x)  [differentiate rate law]

ln \:[\frac{a}{a-x}]=kt \:(Integrated\: rate\: law)

\mathrm{k\: =\: \frac{1}{t}\, ln\left [ \frac{a}{a-x} \right ]}

Unit of k=sec^{-1}

Other Forms of Rate Law

We know that the first-order equation is given as follows:

\mathrm{log_{10}A\: =\: log_{10}A_{o}\: -\: \frac{kt}{2.303}}

But there are other forms of rate law also available that we use for different purposes. These forms are mentioned below:

  • Use to solve numericals:

    \mathrm{log_{10}A\: =\: log_{10}A_{o}\: -\: \frac{kt}{2.303}}

    \mathrm{\Rightarrow log_{10}\left [ \frac{A_{o}}{A} \right]\: =\: \frac{kt}{2.303}}

    \mathrm{Thus, t\: =\: \frac{2.303}{k}\, log_{10}\left [ \frac{A_{o}}{A} \right]}
     
  • Exponential form:

    \mathrm{log_{e}A\: -\: log_{e}A_{o}\: -kt}
    \\\mathrm{\Rightarrow log\frac{A}{A_{o}}\: =\: -kt}\\\\\mathrm{\Rightarrow \frac{A}{A_{o}}\: =\: e^{-kt}}\\\\\mathrm{Thus,\: A\: =\: A_{o}e^{-kt}}
    This equation is also known as exponential form.
Half Life of First Order Reaction

The half-life of a reaction is the time in which the concentration of a reactant is reduced to one half of its initial concentration. It is represented as t1/2.
For a zero order reaction, rate constant is given as:
k=\frac{[\mathrm{R}]_{0}-[\mathrm{R}]}{t}
\text { At } t=t_{1 / 2}, \quad[\mathrm{R}]=\frac{1}{2}[\mathrm{R}]_{0}
The rate constant at t1/2 becomes:

k=\frac{[\mathrm{R}]_{0}-1 / 2[\mathrm{R}]_{0}}{t_{1 / 2}}

t_{1 / 2}=\frac{[\mathrm{R}]_{0}}{2 \mathrm{k}}
It is clear that t1/2 for a zero order reaction is directly proportional to the initial concentration of the reactants and inversely proportional to the rate constant.
For the first order reaction,

k=\frac{2.303}{t} \log \frac{[\mathrm{R}]_{0}}{[\mathrm{R}]}

\text { at } t_{1 / 2} \quad[\mathrm{R}]=\frac{[\mathrm{R}]_{0}}{2}
So, the above equation becomes

k=\frac{2.303}{t_{1 / 2}} \log \frac{[\mathrm{R}]_{0}}{[\mathrm{R}]_{0} / 2}

\text { or } \quad t_{1 / 2}=\frac{2.303}{k} \log 2

t_{1 / 2}=\frac{0.693}{k}

 

Graphs of First Order Kinetics

Study it with Videos

First Order Reaction
Other Forms of Rate Law
Half Life of First Order Reaction

"Stay in the loop. Receive exam news, study resources, and expert advice!"

Get Answer to all your questions

Back to top