Chemical Kinetics Flashcards
For most of the reactions , the value of temperature coeff. lies in between
2 and 3
For 1st order reaction, value of t 1/2 is given by
0.693 / k
For 1st order reaction, the specific reaction constant depends upon
temperature
The rate of chemical reaction depends upon
Active mass
Unit of velocity constant of 1st order reaction
SEC-1
Unit of velocity constant of Zero order reaction
mol litre^ −1 sec^−1
In the reaction between A and B to form C, A represents 1st order and b represents 2nd order . Rate equation will b written as
Rate = k [A] [B]^2
Rate constant of a reaction increases with the increase of which of the following factors
Temperature
Factors on which the rate constant of the 1st order reaction does not depend
Concentration of reactant
Minimum amount of energy required for molecules to react is called
Activation energy
unit of reaction rate is
mol L^-1 s^-1
The rate of a reaction does not depend upon the concentration of the reacting species then the reaction is of _________ order
Zero order
Fast reactions are completed in less than _____ seconds
10^ -9
Unit of rate constant for 3rd order reaction is
mol^-2 litre^2 sec^-1
Difference in the minimum and the maximum energy state of the reactants is called
Activation energy
Rxns which take place by the absorption of radiations are called
Photochemical reactions
The total no. of molecules which participate in a reaction is called
Molecularity
In the mechanism of a reaction, the slowest step is called
Rate determining step
Rate of a reaction is _______ to the concentration of reactant
Proportional
True/False
Every radioactive decay rxn is of 2nd order
False
True/False
half life period of a zero order rxn is inversely proportional to a ( initial conc. )
False
True/False
Order of a rxn is a theoritical step
False
True/False
On decreasing the temp. of a rxn, the half life period also decreases.
False
True/False
for a zero order reaction, half life period is independent of the concentration of the reactant
False
What is Threshold energy
Energy required for the completion of rxn
The minimum amount of energy which the reactant molecules should possess for effective collision.
What is Arrhenius eqn
k = A e ^ -Ea/RT
What is relation b/w threshold energy and activation energy
activation energy = threshold energy - energy of molecules in normal state
What is Quantum efficiency ?
No. of molecules dissociated / no. of photons absorbed
An example of zero order rxn
H2 + Cl2 sunlight⟶2HCl
What is Energy Barrier
the minimum energy achieved by the reactant only after which it can be converted to product is known as Energy barrier. Reactant molecules cannot form activated complex till they reach this height ( activation energy ) and cannot be converted to form product.
Explain the rate determining step
Some chemical reactions complete in one or more steps. Rate of rxn is determined by the slowest step which is known as Rate determining step.
Order of a rxn is zero. Can its molecularity be zero?
MOLECULARITY OF RXN IS ALWAYS A WHOLE NO IT CANNOT BE 0
What is specific rxn rate ?
Specific rxn rate of a rxn at a given temp. is equal to that rate of a rxn when concentration of each reactant is unity.
Eg :- For R = k [A][B]
if A = B = 1 , then
rate of rxn = k ; where k is specific rxn rate constant.
When is avg rate of rxn equal to its instantaneous rate ?
Instantaneous rate and average rate of a reaction are same when Δt→0.
What are pseudo unimolecular rxns ?
In a chemical reaction if two or more reactants are involved but the rate of reaction depends only upon the concentration of any one of the reactant and independent of other reactants then it is said to be pseudo uni molecular reaction.
Eg. 1. Acid Catalyzed Hydrolysis of ester.
2. Inversion of Sucrose ( it is a 1st order rxn)
What is temperature coeff. ?
The temperature coefficient of reaction IS the factor by which rate constant of reaction gets increased on increasing the temperature by 10°C.
temperature coefficient = K(at temp. t+10) / K (t) = 2 to 3
Generally, this range is taken from 25°C to 35°C, by convention.
What is order of rxn ?
The order of a rxn is defined as the sum of all the powers to which the concentration terms in the rate law are raised to express the observed rate of the rxn.
Write about rate of rxn .
it is expressed in terms of consumption of reactants or in terms of formation of product per unit time.
it depends on conc. of reactant at a particular moment
it generally decreases with the progress of rxn.ITS UNIT IS MOL L-1 CM-1
Write about rate constant .
it is proportionality constant in different forms in rate law or rate equation
it is independant of concn. of reactant.
it does not depend on the progress of rxn.
Write a short note on Activation energy.
Activation energy is defined as the minimum amount of extra energy required by a reacting molecule to get converted into a product.
It can also be described as the minimum amount of energy needed to activate or energise molecules or atoms so that they can undergo a chemical reaction or transformation.
Write few factors which affect the rate of a chem. rxn
Conc. of reactants
Temp. of system
Presence of catalyst
Nature of the reactants
Exposure to radiations
The expression representing rate of rxn
Change in conc. of reactant (or product ) / Change in time
Molecularity of a rxn
The number of reacting particles (molecules, atoms, or ions) that collide simultaneously in a rate determining step to form a product is called molecularity of a reaction.
In general, the molecularity of simple reactions is equal to the sum of the number of molecules of reactants involved in the balanced stoichiometric equation.
Hydrolysis of sucrose to glucose and fructose Sucrose + H2O =Glucose + Fructose. is an example of
a first order rxn
What is instantaneous rate of rxn
The instantaneous rate is the rate of a reaction at a period of time that is so short that the concentrations of reactants and products change by a negligible amount.
The instantaneous rate of reaction can be expressed as the rate of decrease in a concentration of reactants or the rate of increase in the concentration of products.
2N2O3 → 4NO2 + O2 is 1st order rxn, why ?
In this rxn, when graph is plotted b/w rate of rxn and then again graph is plotted b/w rate of rxn and [N2O3]^2 , it is shown that in the first graph a straight line is obtained.
Rate = k[N2O3]
Therefore it is a 1st order rxn.
H2 + I2 → 2HI is a 2nd order rxn. Why ?
In this rxn, when a graph is plotted b/w rate of rxn and [H2] and [I2] a straight line is obtained.
Rate = k [H2][I2]
therefore it is a 2nd order rxn.
Half life period for 1st order rxn if k = 5.5 x 10^-14 sec^-1 is :
1.16 x 10 ^ 13 sec
A FIRST ORDER RXN GETS COMPLETED TO 75% IN 32 I HOW MUCH TIME WOULD HAVE BEEN REQUIRED FOR 50 % COMPLETION
16 MIN
ARRHENIUS EQ
K = A e -Ea/RT
ORDER OF RXN FOR RATE =K[A]1/2[B]3/1
2
HALF LIFE PERIOD OF RADIOACTIVE ELEMENT IS 140 DAYS . ON TAKING 1 GM ELEMENT INITALLY THE AMOUNT LEFT AFTER 560 DAYS WILL BE
1/16GM
FOR A 0 ORDER RXN
dx/dt = k[A]
THE DIFFERANCE BETWEEN MAX AND MINI ENERGY STATE OF RXN
ACTIVATION ENERGY
THRESOLD ENERGY
ENERGY REQ FOR COMPLETION OF RXN
