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The minimum excess energy which must be supplied to reacting species to cross the energy barrier. 

K= Ae^-Ea/RT

K= rate constant , A = frequency factor

(i) Order - Zero, Molecularity - Two

(ii) Units of k-mol L^-1 s^-1

(i) Order of a reaction is meant for elementary as well as for complex reactions but molecularity is for elementary reactions. 

(ii) Order can be zero or fraction but molecularity cannot be zero or fraction.

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The chemical thermodynamics studies the chemical equilibrium as a source of work and heat etc. The kinetics also has its specific approach to the chemical reaction. It studies the chemical transformation as a process that occurs in time according to a certain mechanism with regularities characteristics of this process.

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Bimolecular reaction becomes kinetically first order when one of the reactants is in excess.

The rate of a reaction depends on the concentration of reactants. As the reaction progresses, reactants start getting converted to products so the concentration of reactants decreases hence the rate decreases.

Thermodynamically the conversion of diamond to graphite is highly feasible but this reaction is very slow because its activation energy is high.

The reaction between KMnO₄ and oxalic acid is very slow. By raising the temperature we can enhance the rate of reaction.

Activation energy for the combustion reaction is very high and is not available at room temperature. OH applying flame, to a part of the coal and air in contact with the flame absorb heat which provides the necessary activation energy and combustion starts. The heat liberated further provides activation energy for the combustion to continue.

Suppose initially the concentration are [NO^-₂] = a mol L^-1, [I^-] = b mol L^-1 and [H⁺ ] = c mol L^-1 

∴ Rate = K abc² 

(i) New [H⁺] = 2c 

∴ New rate = 4ab (2c)² = 4abc² 

= 4 times 

(ii) New [I^-] = \(\frac{b}{2}\)

New Rate = Ka \(\frac{b}{2}\)c² = \(\frac{1}{2}\)Kabc² 

ie. rate of reaction is halved 

(iii) New [NO^-₂] = 3a, [I^-] = 3b, [H⁺] = 3c 

New rate = K (3a) (3b) (3c)² 

= 81K abc² = 81 times.

Option : (b) mol dm^-3t^-1

‘m’ is the mass of the adsorbent and ‘x’ is the number of moles of the adsorbate when the dynamic equilibrium has been achieved between the free gas and the adsorbed gas. 

(a) y = 2x.This is because for 3/4 ^th of the reaction to complete, time required = two half lives.

(b) This is because of improper orientation of the colliding molecules at time of collision.

Many reactions take place in a series of steps. Such reactions are called complex reactions. Each step taking place in a complex reaction is called an elementary reaction. This shows that a complex reaction is broken down in a series of elementary chemical reactions.

By adding all the elementary steps of a complex reaction we get the overall reaction.

The mechanism of a reaction is decided from the sequence of the elementary steps that are added to give overall reaction.

Elementary reaction : It is defined as the reaction which takes place in a single step and cannot be divided further into simpler chemical reactions.

The order and molecularity of the elementary reaction are same.

Some reactions take place in one step and cannot be broken down into simpler reactions.

For example,

C₂H₅I_(g) → C₂H_4(g) + HI_(g)

O_3(g) → O_2(g) + O_(g)

(i) Order is same as molecularity.

(iv) Molecularity can never be zero.

(iii) Assertion is correct but reason is incorrect.

(ii) Both assertion and reason are correct but reason does not explain assertion. 

(i) reverse reaction is involved.

(iii) it is a sequence of elementary reactions.

(iv) any of the reactants is in excess.

(ii) determining the rate constants at two temperatures.

atms^-1 or bars^-1

The rate of a reaction generally increases with increase in temperature. For a chemical reaction with every rise in temperature by 10° ,the rate of the most reactions is almost doubled.

 K= Ae^-Ea/RT

Different reactions has different activation energy.

According to the rates of the reactions, they can be classified as : 

(1) Fast reactions, 

(2) Very slow reactions, 

(3) Moderately slow reactions.

(1) Fitst actions : In this, reactants react almost instantaneously, e.g., neutralisation reaction between H⁺ and OH^-, forming water.

H+(xa) + OH-(aq) → H₂O_0D

(2) Very slow reactions : In this, the reactants react extremely slow, so that there is no appreciable change in the concentrations of the reactants over a long period of time. 

E.g., reaction of silica with mineral acids, rusting of iron, etc.

(3) Moderately slow reactions : In this, the reactants react moderately slow with a measurable velocity, 

e.g., the hydrolysis of the esters.

CH₃COOC₂H₅ + H₂O \(\overset{H^+}\longrightarrow\) CH₃COOH + C₂H₅OH

• It deals with the study of the rates and mechanism of reactions.
• The effect of temperature on the reaction rates can be studied. 
• The influence of catalysts can be studied. 
• The conditions for altering the rates and mechanisms of chemical reactions can be predicted. 
• Thermodynamic parameters like energy, enthalpy changes, Δ5, ΔG of the reactions can be calculated. 

Chemical kinetics is a branch of physical chemistry which involves the study of the rates and mechanisms of chemical reactions and the influence of various factors like temperature, pressure, catalyst, etc., on the rates of reactions.

Different ways to determine order of a reaction from:

(i) Rate law- The sum of powers of all the conc. terms is equal to the order of the reaction. It May be zero or even fractional. 

(ii) Unit of K- For zero order reaction unit of K is mol L^-1 sec^-1 , for 1st order reaction unit of K is sec^-1, for 2nd order reaction unit of K is mol^-1 L sec^-1  

(iii) Initial rate method- A chemical reaction is carried out with different initial conc. of each reactant and rate of reaction is determined in each case. The rate law is written in each Case. Rate laws are divided suitably to get the value of powers raised to each conc. terms in rate law. 

(iv) Integrated equation- In this method integrated rate equations for zero, first & second order reaction are used for given data. If the value of K comes to be constant, putting different time& concentration, using a particular expression so the reaction follow that order. 

(v) Half life period- Knowing the time required for the completion of 50% of the reaction we can identify the order of the reaction. t_1/2 for zero order reaction is directly proportional to the initial conc. of the reactant, t_1/2 for 1st order reaction is independent of initial conc. of the reactant. 

(vi) From reaction mechanism- For a complex reaction different steps are written. (Or from given reaction mechanism). The slowest step is identified; the order of over all reaction is equal to the no. of conc. terms involved in the slowest step. 

(a) Given : 

A + B → Products 

The reaction is zero order in A and second order in B. 

Hence the rate law is represented as, 

Rate = k [A]⁰ [B]²

Rate = k[B]²

(b) Given : 

2NO_(g) + Br_2(g) → 2NOBr_(g) 

The reaction is second order in NO and first in Br₂. 

Hence the rate law is, 

∴ Rate = k [NO]² [Br₂]

∴ (a) Rate law : Rate = k[B]²

(b) Rate law : Rate = k [NO]² [Br₂]

Where E_a is the energy of activation for the reaction. When a graph is plotted for log K versus \(\frac{1}{T}\), a straight line with a slope 6670 K is obtained.

Calculate the energy of activation for this reaction. State units (R = 8.314 JK^-1 mol^-1)

Slope of the line

\(\frac{-E_a}{2.303 R}\) = -6670 K 

E_a = 2.303 × 8.314 (JK^-1 mol^-1) × 6670 K 

= 127711.4 J mol^-1.

(i) Zero (ii) –k (iii) mol L^–1s^–1

At higher temperatures, larger fraction of colliding particles can cross the energy barrier (i.e. the activation energy), which leads to faster rate.

This is because activation energy for the reaction is very high at room temperature.

The probability of more than three molecules colliding simultaneously is very small. Hence possibility of molecularity being three is very low.

Molecularity is the number of molecules taking part in an elementary step. For this we require at least a single molecule leading to the value of minimum molecularity of one.

(iii) The order of a reaction is always equal to the sum of the stoichiometric coefficients of reactants in the balanced chemical equation for a reaction.

(i) area under the curve must not change with increase in temperature.

(iv) with increase in temperature curve broadens and shifts to the right hand side.

(ii) (V₄ - V₂)/(50 - 30)

If the reaction is an elementary reaction, order is same as molecularity.

(i) Rate of a reaction increases with increase in temperature.

(ii) Rate of a reaction increases with decrease in activation energy.

(i) The rate of a reaction decreases with passage of time as the concentration of reactants dereases.

(i) Rate = k [NO]²
Order of reaction = 2
Unit of rate constant = (mol L^-1)^1-n x s^-1
n = order of reaction = (mol L^-1)^1-2 x s^-1 = L mol^-1 s^-1
Hence order of above reaction is 2 and its unit is L mol^-1 s^-1.
(ii) Rate = k [H₂O_g][I^–]
Order of reaction = 1 + 1 = 2
Unit of rate constant = (mol L^-1)^{1 – n} x s^-1
= (mol L^-1)^{1 – 2} x s^-1
= (mol L^-1) x s^-1 = L mol^-1 x s^-1
For the reaction order is 2 and unit of rate constant is L mol^-1 s^-1
(iii) Rate = k (CH₃CHO)^{\(\frac { 3 }{ 2 }\)}
Order of reaction= \(\frac { 3 }{ 2 }\)
Unit of rate constant = (mol L^-1)^{1 – 15} x s^-1 = mol^-1/2 L^1/2 s^-1
(iv) Rate = k [C₂H₅CI]
Order of reaction = 1
Unit of rate constant = (mol L^-1)^{1 – n} x s^-1 = s^-1
Order is 1 and unit is s^-1

(ii) Catalyst raises the activation energy.

(iv) Catalyst alters enthalpy change of the reaction.

Rate = k [A]⁰[B]⁰ or Rate = k

According to Arrhenius equation K = Ae^-Ea/RT 

Given K = (4.5 × 10¹¹s^-1)\(e \frac{-28000K}{T}\)

comparing the two equations

\(\frac{E_a}{RT} = \frac{-28000K}{T}\)

E_a = 28000 × R 

= 28000 × 8.314 J mol^-1 

= 232.79 KJ mol^-1