Assignment chemical equilibrium JH sir 4168 kho tài liệu bách khoa

I Effect of change of concentration :Increase in concentration of reactant propel the reaction in forward direction and increase in concentration of product propel the reaction in backwa

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CHEMICAL EQUILIBRIUM

Types of chemical reactions

Types of chemical reactionsIrreversible reaction Reversible reaction

1 The reaction which proceeds in one direction (forward

direction) only.

1 The reaction which proceed in both the direction under the same set of experimental conditions.

2 Reactants are almost completely converted into products.

Products do not react to form reactants again.

2 Reactants form products and products also react to form reactants

in backward direction These are possible in closed vessels

3 Do not attain equilibrium state 3 Attain the equilibrium state and never go to completion.

4 Such reactions are represented by single arrow {} 4 Represented by double arrow ( ) or

(a) Precipitation reactions e.g

NaCl(aq) + AgNO 3 (aq)  NaNO 3 (aq) + AgCl 

(a) Homogeneous reactions- only one phase is present

(b) Neutralization reactions e.g

HCl(aq) + NaOH(aq)  NaCl(aq) + H 2 O

(c) 2KClO 3 (s) 2KCl(s) + 3O 2 (g)

(d) Reactions in open vessel : –

Even a reversible reaction will become irreversible if it is

carried out in open vessel Ex.

(ii) Liquid phase

CH 3 COOH(l) + C 2 H 5 OH(l) CH 3 COOC 2 H 5 (l)+ H 2 O(l) Heterogeneous reactions– More than one phases are present CaCO 3 (s) CaO(s) + CO 2 (g)

NH 4 HS(s) NH 3 (g) + H 2 S(g) Closed

vessel

Open vessel

STATE OF CHEMICAL EQUILIBRIUM :

At equilibrium :

(i) Rate of forward reaction (rf) = rate of backward reaction (rb) (dynamic nature)

(ii) All measurable parameters become constant with respect to time

Types of equilibria on the basis of process

Types of equilibria on basis of physical state



Homogeneous equilibrium Heterogeneous equilibrium

When all reactants and products When more than one phase are

H2(g) + Cl2(g) 2HCl(g) 3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g)

SO2(g) + NO2(g) SO3(g) + NO(g) 2Na2O2(s) + 2H2O() 4NaOH + O2(g)

CHARACTERISTICS OF CHEMICAL EQUILIBRIUM :

The nature and the properties of the equilibrium state are the same regardless of the direction from which it

is achieved It can be achieved in both directions

Equilibrium is dynamic in nature

It means that at microscopic level reaction has not stopped It appears that no change is occuring but Butboth the opposing reactions are proceeding at the same rate So there is no net change.Thus equilibrium isnot static in nature

A catalyst can alter the rate of approach of equilibrium but does not change the state of equilibrium By usingcatalyst, the equilibrium can be achieved in different (more/less) time, but the relative concentrations ofreactants and products are same irrespective of the presence or absence of a catalyst

Equilibrium can be observed by constancy of some observable properties like colour, pressure, concentration,density, temperature, refractive index etc.which may be suitable in a given reaction

At equilibrium, free energy changeG = 0

Equilibrium state can be affected by altering factors like pressure, volume, concentration and temperatureetc.(Le chateliers Principle)

System moves toward an equilibrium state spontaneously even if it is disturbed It will return to original state

LAW OF MASS ACTION :

To illustrate the law of mass action, consider the following general reaction at constant temperature,

a b r

k [C] [D]

k  [A] [B]

or

c d f

Where, Kc is the equilibrium constant in terms of molar concentration

Equilibrium Constant (Kp) in terms of Partial Pressures:

Applications of Equilibrium constant :

Predicting the direction of the reaction

]D[]C[

at any time during reaction is called reaction quotient.The concentrations[C], [D] , [A], [B] are not necessarily at equilibrium

Predicting the extent of the reaction :

K =

eq

eq]tanac[Re

]oduct[Pr

Case-I If K is large (K > 103) then product concentration is very very larger than the reactant ([Product] >>[Reactant])

Hence concentration of reactant can be neglected with respect to the product In this case, the reaction isproduct favourable and equilibrium will be more in forward direction than in backward direction

Case-II If K is very small (K < 10–3)

[Product] << [Reactant]

Hence concentration of Product can be neglected as compared to the reactant

In this case, the reaction is reactant favourable

Equilibrium constant is dependent only on the temperature.

It means Kp and Kc will remain constant at constant temperature no matter how much changes are made inpressure, concentration, volume or catalyst

However if temperature is changed,

1

; H = Enthalpy of reaction

If T2 > T1 then K2 > K1 provided H = +ve (endothermic reaction)

K2 < K1 if H = –ve (exothermic reaction)

In the above equation, the unit of R and H/T should be same

Relation between equilibrium constant & standard free energy change.

Gº = – 2.303 RT log K

Where G° = standard free energy change

T = Absolute temperature,

R = universal gas constant

Homogeneous liquid system : Formation of ethyl acetate :

The reaction between alcohol and acid to form ester is an example of homogeneous equilibrium in liquidsystem

CH3COOH(l) + C2H5OH(l) CH3COOC2H5(l) + H2O(l)

KC = [[CHCHCOOHCOOC][CH H][HOHO]]

5 2 3

2 5 2 3

Observed molecular weight and Observed Vapour Density of the mixture

mequilibriuat

molesof.nototal

)g(Aofweight

=

))1n(1(a

M

Mn A





 , MAn = Molar mass of gas AAn

Vapour density (V.D) : Density of the gas divided by density of hydrogen under same temp &

pressure is called vapour density

 D = vapour density without dissociation =

MMd)1n(

dD

where MT = Theoritical molecular wt M0 = observed molecular wt or molecular wt of the mixture at equilibrium

EXTERNAL FACTORS AFFECTING EQUILIBRIUM :

(I) Effect of change of concentration :

Increase in concentration of reactant propel the reaction in forward direction and increase in concentration

of product propel the reaction in backward direction

(II) Effect of change of pressure :

(a) When n = 0 ; no effect

(b) When n  0 ;

If pressure increases the reaction shifts in the direction of lesser number of moles

If pressure decreases the reaction shifts in the direction of greater number of moles

(III) Addition of inert gas :

(a) At constant volume – no effect

(b) At constant pressure –

When n = 0 ; no effectWhen n  0 ;Reaction shifts in the direction of greater number of moles.

(IV) Effect of temperature :

(a) If H = +ve (endothermic) an increase in temperature, shifts the reaction in forward direction and vice–versa

(b) If H = –ve (exothermic) an increase in temperature, shifts the reaction in backward direction and vice–versa

Application of Le-Chatelier Principle to Physical Equilibrium :

(1) Effect of Pressure on Melting Points :

(a) When volume of solid decrease on melting i.e., in liquid state volume is lesser, then by increasing pressure

on such solids the melting point will go down, because at high pressure melting is facilitated eg Ice,diamond, Carborundum (SiC) etc

Solid Liquid

(b) When volume increase on melting then by increasing pressure, the above equilibrium will shift in the reverse

direction, hence process of melting will be lowered and more heat is required, thus melting point will rise

eq Iron, Copper, NH4Cl, NaCl etc

(2) Effect of Pressure on Boiling point :

When pressure is raised then condensation of vapour into liquid take place, thus vapour pressure willdecrease Now more heat is required to equate vapour pressure with atmospheric pressure, hence boilingpoint will increase

FREE ENERGY AND CHEMICAL EQUILIBRIUM :

place between gaseous reactants and products represented by the general equation

aA + bB cC + dDAccording to Van’t Hoff reaction isotherm

G = 0Thus at equilibrium

PART - I : OBJECTIVE QUESTIONS

Section (A) : Equilibrium, Equilibrium constant ,law of mass action, Reaction Quotient

A-1. A chemical reaction, A B, is said to be in equilibrium when :

(A) rate of forward reaction is equal to rate of backward reaction

(B) conversion of A to B is only 50% complete

(C) complete conversion of A to B has taken place

(D) only 25% conversion of A to B taken place

A-2. The equilibrium concentration of x, y and yx2 are 4, 2 and 2 respectively for the equilibrium

2x + y yx2 The value of equilibrium constant, KC is

A-4. For the following reaction at 250°C, PCl3(g) + Cl2(g) PCl5(g) the value of KC is 26 then the value of Kp

at same temperature will be

A-5. For a reversible reaction, the rate constants for the forward and backward reactions are

2.38 ×10–4 and 8.15 × 10–5 respectively The equilibrium constant for the reaction is –

A-6. If different quantities of ethanol and acetic acid were used in the following reversible reaction,

CH3COOH() + C2H5OH() CH3COOC2H5() + H2O()the equilibrium constant will have values which will be ?

(A) different in all cases

(B) same in all cases

(C) higher in cases where higher concentration of ethanol is used

(D) higher in case where higher concentration of acetic acid is used

A-7. Chemical equilibrium is dynamic in nature because –

(A) The equilibrium in maintained quickly

(B) Conc of reactants and products become same at equilibrium

(C) Conc of reactants and products are constant but different

(D) Both forward and backward reactions occur at all times with same speed

A-8. Which of the following statements is false in case of equilibrium state –

(A) There is no apparent change in properties with time

(B) It is dynamic in nature

(C) It can be attained from either side of the reaction

(D) It can be attained from the side of the reactants only

A-9. Starting with the reactants , At any moment before a reversible reaction attains equilibrium it is found

that –

(A) The rate of the forward reaction is increasing and that of backward reaction is decreasing(B) The rate of the forward reaction is decreasing and that of backward reaction is increasing(C) The rate of both forward and backward reactions is increasing

(D) The rate of both forward and backward reactions is decreasing

A-10. A chemical reaction A B is said to be in equilibrium when

-(A) Complete conversion of A to B has taken place

(B) Conversion of A to B is only 50% complete

(C) Only 10% conversion of A to B has taken place

(D) The rate of transformation of A to B is just equal to rate of transformation of B to A in the system

A-11. In a chemical reaction Kp is greater than Kc when

(A) the number of molecules entering into the chemical reaction is more than the number of moleculesproduced

(B) the number of molecules entering into the chemical reaction is the same as the number of moleculesproduced

(C) the number of molecules entering into the chemical reaction is less than the number of moleculesproduced

(D) the total number of moles of reactants is less than the number of moles of products

(A) Its value does not depend upon the initial conc of the reactants

(B) Its value does not depend upon the initial conc of the products

(C) Its value does not depend upon temperature

(D) Its value does not depend upon presence of catalyst

reaction is 3.2 × 10–2, the rate constant of forward reaction is

A-15. The value of KP for the reaction H2(g) + I2(g) 2HI(g) is 50 What is the value of KC

-a b

C(  )2

(C) KP = KC RT (D) KP = KC

of KP is

-(A) 2.936 atm (B) 0.0625 atm (C) 6.25 atm (D) 0.00625 atm

A-19. The reaction A(g) + B(g) C(g) + D(g) proceeds to right hand side upto 99.9% when starting bwith

equal moles of A and B The equilibrium constant K for the reaction will be

A-20. For the reaction, 2NO2 (g) 2NO (g) + O2(g), KC = 1.8 × 10–6 at 185ºC At 185ºC, the

value of KC for the reaction

-NO(g) + 1

2O2 (g) NO2(g) is (A) 0.9 × 106 (B) 7.5 × 102 (C) 1.95 × 10–3 (D) 1.95 × 103

-A-21. If in the reaction N2O4(g) 2NO2(g),  is the part of N2O4 which dissociates per mole, then the

number of moles at equilibrium will be

A-24. For the reaction A(g) + B(g) C(g) + D(g), the degree of dissociation  would be –

(A)

1K

(A) KP = KC (B) KP = KC RT (C) KP = KC (R T)–2 (D) KP = KC (R T)–1

C2H4(g) + H2(g) C2H6(g), the equilibrium constant can be expressed in units of

-(A) litre–1 mol–1 (B) mol2 litre–2 (C) litre mol–1 (D) mollitre–1

A-28. Equilibrium concentration of HI, I2 and H2 is 0.7, 0.1 and 0.1 moles/litre Calculate the equilibrium

constant for the reaction :

(A) Mole–1 litre (B) Mole–2 litre (C) Molelitre (D) None

A-33. In Which of the following equilibria, the value of KP is less than KC

-(A) H2 + I2 2Hl (B) N2 + 3H2 2NH3

(C) N2 + O2 2NO (D) CO + H2O CO2 + H2

equilibrium concentrations are ( a  x) and (b + x) respectively; express x in terms of k1, k2, a and b

(A)

2 1

2 1

kk

bka

2 1kk

bkak





(C)

2 1

2 1kk

bka

k 

(D)

2 1

2 1kk

bkak





constant of the reaction 2SO3(g) 2SO2(g) + O2(g) would be :

(A) 250 atm (B) 4 × 103 atm (C) 0.25 × 104 atm (D) 6.25 × 104 atm

Section (B) : Degree of Dissociation, Vapour Density , Average Molar Mass

B-1. For which of the following reactions, the degree of dissociation cannot be calculated from the vapour density

data

I 2H(g)  H2(g) + I2(g) II 2NH3(g)  N2(g) + 3H2(g)

III 2NO(g)  N2(g) + O2(g) IV PCl5(g)  PCl3(g) + Cl2(g)

(A) I and III (B) II and IV (C) I and II (D) III and IV

B-2. The degree of dissociation of SO3 is  at equilibrium pressure P0

Kp for 2SO3(g) 2SO2(g) + O2(g) is

(A) [(P03)/2(1 – )3] (B) [(P03)/(2+)(1 – )2]

(C) [(P02)/2(1 – )2] (D) None of these

B-3. In a container equilibrium N2O4 (g) 2NO2 (g)

is attained at 25°C The total equilibrium pressure in container is 380 torr If equilibrium constant of aboveequilibrium is 0.667 atm, then degree of dissociation of N2O4 at this temperature will be :

(A)

3

1

(B) 2

1

(C) 3

2

(D) 41

B-4. In the dissociation of N2O4 into NO2, (1 + ) values with the vapour densities ratio 

B-5. In the above question,  varies with

d

D according to :

B-6. Before equilibrium is set-up for the chemical reaction N2O4(g) 2NO2(g), vapour density d of thegaseous

mixture was measured If D is the theoretical value of vapour density, variation of  with D/d is given by thegraph What is value D/d at point A?

B-7. The degree of dissociation of PCl5 () obeying the equilibrium, PCl5 PCl3 + Cl2 , is approximately

related to the presure at equilibrium by (given  << 1) :

B-8. For the reaction N2O4 (g) 2NO2 (g), if percentage dissociation of N2O4 are 20%, 45%, 65% & 80%,

then the sequence of observed vapour densities will be :

(A) d20 > d45 > d65 > d80 (B) d80 > d65 > d45 > d20

(C) d20 = d45 = d65 = d80 (D) (d20 = d45) > ( d65 = d80)

B-9. An unknown compound A dissociates at 500ºC to give products as follows

-A(g) B(g) + C(g) + D(g)Vapour density of the equilibrium mixture is 50 when it dissociates to the extent to 10% What will

be the molecular weight of Compound A –

a density of 41 What will be the degree of dissociation

of PCl5–

Section (C) : Le Chateliers Principle

C-1. Consider the reaction, CaCO3(s) CaO(s) + CO2(g) ; in closed container at equilibrium What

would be the effect of addition of CaCO3 on the equilibrium concentration of CO2

(C) Remains unaffected (D) Data is not sufficient to predict it

C-2. In the melting of ice, which one of the conditions will be more favourable –

(A) High temperature and high pressure (B) Low temperature and low pressure

(C) Low temperature and high pressure (D) High temperature and Low pressure

C-3. In the reaction, 2SO2 (g) + O2 (g) 2SO3 (g) + X cals, most favourable condition of temperature

and pressure for greater yield of SO3 are

-(A) Low temperature and low pressure (B) High temperature and low pressure

(C) High temperature and high pressure (D) Low temperature and high pressure

C-4. On adding inert gas to the equilibrium PCI5(g) PCI3(g) + CI2(g) at constant pressure The degree

of dissociation will remain –

C-5. Dissociation of phosphorus pentachloride is favoured by –

(A) High temperature and high pressure (B) High temperature and low pressure

(C) Low temperature and low pressure (D) Low temperature and high pressure

C-6. Adding inert gas to system N2(g) + 3H2(g) 2NH3(g) at equilibrium at constant volume will lead to :

(A) N2 and H2 are formed in abundance

(B) N2, H2 and NH3 will have the same molar concentration

(C) The production of ammonia increases

(D) No change in the equilibrium

C-7. In the reaction N2(g) + 3H2(g) 2NH3(g), the forward reaction is exothermic and the backward

reaction is endothemic In order to produce more heat it is necessary –

(A) To add ammonia

(B) To add N2 and H2

(C) Increasing the concentration of N2,H2 and NH3 equally

(D) None of the above

C-8. The reaction in which the yield of the products can not be increased by the application of high pressure

is –

(A) PCl3 (g) + Cl2 (g) PCl5 (g) (B) N2 (g) + 3H2 (g) 2NH3 (g)

(C) N2 (g) + O2 (g) 2NO(g) (D) 2SO2 (g) + O2 (g) 2SO3 (g)

C-9. Factors affecting KC is/are

-(A) Increasing concentration of the reactant

(B) Presence of catalyst

(C) Method of writing balanced equation (or stoichiometry of reaction)

(D) Time taken by the chemical reaction

-(A) Increase in pressure (B) Decrease in pressure

(C) Neither increase nor decrease in pressure (D) Data unpredictable

3 A(g) + B(g) 4C(g) + heat

(A) Increase in pressure (B) Increase in volume

(C) Increase in temperature (D) Decrease in temperature

-(A) Value of Kp decreases

(B) Value of Kp increases

(C) The degree of dissociation of HI decreases

(D) Degree of dissociation of HI increases

C-13. For the reaction PCl5 (g) PCl3 (g) + Cl2 (g), the forward reaction at constant temperature is

favoured by

-(A) Increasing the volume of container

(B) Introducing an inert gas at constant pressure

(C) Introducing PCl5 at constant volume

(D) All of these

-(A) H2(g) + I2(g) 2HI(g) (B) N2(g) + 3H2(g) 2NH3(g)

(C) PCl5(g) PCl3(g) + Cl2(g) (D) N2(g) + O2(g) 2NO(g)

-(A) Shift in the forward direction (B) Shift in the reverse direction

(C) Increase in the yield of H2 (D) No effect

C-16. Which of the following will shift the reaction PCl3(g) + Cl2(g) PCl5(g) to the left

side-(A) Addition of PCl5 (B) Increase in pressure

(C) Decrease in temperature (D) Catalyst

-(A) N2 (g) + O2 (g) 2NO(g) (B) 2SO2 (g) + O2 (g) 2SO3(g)

(C) 2O3 (g) 3O2(g) (D) 2NO2 (g) N2O4(g)

C-18. According to Le Chatelier principle, an increase in the temperature of the following reaction will

N2 + O2 2NO – 43200 cal

(A) Increase the yield of NO (B) Decrease the yield of NO

(C) Not effect on the yield of NO (D) Not help the reaction to proceed

-(A) The forward reaction stops

(B) The backward reaction stops

(C) The whole reaction stops

(D) The forward and backward reaction proceed with same speed

(C) Will be decreased (D) Some times increases some times decreases

can be increased by :

(A) adding a suitable catalyst (B) adding an inert gas

(C) decreasing the volume of container (D) increasing the amount of CO(g)

C-22.* For the reaction : PCl5 (g) PCl3 (g) + Cl2 (g)

The forward reaction at constant temperature is favoured by

(A) introducing chlorine gas at constant volume

(B) introducing an inert gas at constant pressure

(C) increasing the volume of the container

(D) introducing PCl5 at constant volume

is added to the system Predict which of the following facts will be affected

(A) More NH3(g) is produced (B) Less NH3(g) is produced

(C) No affect on the equilibrium (D) Kp of the reaction is decreased

(A) The pressure changes do not affect the equilibrium

(B) More of ice melts if pressure on the system is increased

(C) More of liquid freezes if pressure on the system is increased

(D) The pressure changes may increase or decrease the degree of advancement of the reaction dependingupon the temperature of the system

(A) Decrease in temperature

(B) Increase in pressure

(C) Decrease in pressure suddenly which results in decrease of solubility of CO2 gas in water

(D) None

helium, is introduced at constant volume Which of the following statement(s) is/are correct

(A) Concentrations of SO2, Cl2 and SO2Cl2 are changed

(B) No effect on equilibrium

(C) Concentration of SO2 is reduced

(D) Kp of reaction is increasing

C-27. An equilibrium mixture in a vessel of capacity 100 litre contain 1 mol N2, 2 mol O2 and 3 mol NO Number of

moles of O2 to be added so that at new equilibrium the conc of NO is found to be 0.04 mol/lit.:

(A) (101/18) (B) (101/9) (C) (202/9) (D) None of these

Above equilibrium is established by taking some amount of CaSO4(s) in a closed container at 1600 K Thenwhich of the following may be correct option

(A) moles of CaO(s) will increase with the increase in temperature

(B) If the volume of the container is doubled at equilibrium then partial pressure of SO2(g) will change at

(A) low temperature and high pressure (B) high temperature and high pressure

(B) low temperature and low pressure (D) high temperature and low pressure

N2(g) + 3H2(g) 2NH3(g) + 22.4 kcal

the maximum yield of ammonia will be obtained when the process is made to take place –

(A) at low pressure and high temperature (B) at low pressure and low temperature

(C) at high pressure and high temperature (D) at high pressure and low temperature

pressure for greater yield of SO3 are :

(A) low temperature and low pressure (B) high temperature and low pressure

(C) high temperature and high pressure (D) low temperature and high pressure

two mole each of A and B were taken into a flask The following must always be true when the systemattained equilibrium :

(A) [A] = [B] (B) [A] < [B] (C) [B] = [C] (D) [A] > [B]

increases while tem perature and volum e remain the sam e According to the

Le Chatelier’s principle, the dissociation of SO3 :

(A) increases (B) decreases (C) remains unaltered (D) change unpredictably

helium, is introduced Which of the following statements is correct ?

(A) concentrations of SO2Cl2, SO2 and Cl2 do not change

(B) more Cl2 is formed

(C) concentration of SO2 is reduced (D) more SO2Cl2 is formed

Section (D) : Simultaneous Equilibrium

D-1. The two equilibria, AB(aq) AA+(aq) + B(aq) and AB(aq) + B(aq) AB2(aq) are simultaneously

maintained in a solution with equilibrium constants, K1 and K2 respectively The ratio of concentration of A+

to AB2 in the solution is :

(A) directly proportional to the concentration of B– (aq.)

(B) inversely proportional to the concentration of B– (aq.)

(C) directly proportional to the square of the concentration of B– (aq.)

(D) inversely proportional to the square of the concentration of B– (aq.)

D-2. In the preceeding problem, if [A+] and [AB2] are y and x respectively, under equilibrium produced by adding

the substance AB to the solvents, then K1/K2 is equal to

y2 

(C)

x

)yx(

y2 

(D) (x y)xy



D-3.* The two equilibrium, AB AA + B and AB + B AB2 are simultaneously maintained in a solution

with equilibrium constants, K1 and K2 respectively If [A+] and [AB2] are y and x respectively, under equilibriumproduced by adding the substance AB(s) to the solvents, then

 (C) [B¯]eq. = y – x (D) None of these

Section (E) : Thermodynamics of Equilibrium

E-1. Which is/are correct relation (s) for thermodynamic equilibrium constant

(A) Gº = –2.303 RT log K (B) G = Gº + 2.303 RT log K

(C) Eºcell =

n

0591 0

n

0591 0

logK

E-2. Which is/are correct relation (s) for equilibrium constant K?

(A) Gº = – 2.303 RT log K (B) Ecellº =

nF

K log RT 303 2

(C) K = Ó [ Pr oduct]

Ó [ Re ac tan t] (D) log K = log A –

RT 2.303

H



E-3. For the reaction H2(g) + I2(g) 2HI(g)

Kc = 66.9 at 350°C and Kc = 50.0 at 448°C The reaction has

E-4. Variation of log10 K with

T

1

is shown by the following graph in which straight line is at 45°, hence H° is :

(A) + 4.606 cal (B) – 4.606 cal (C) 2 cal (D) – 2cal

1

then,(A) K2 > K1 if T2 > T1 for an endothermic change

(B) K2 < K1 if T2 > T1 for an endothermic change

(C) K2 > K1 if T2 > T1 for an exothermic change

(D) K2 < K1 if T2 > T1 for an exothermic change

E-6. Which one of the following oxides is most stable? The equilibrium constants are given at the same temperature:

(A) 2N2O5(g) 2N2(g) + 5O2(g) ; K = 1.2 × 1034

(B) 2N2O(g) 2N2(g) + O2(g) ; K = 3.5 × 1035

(C) 2NO(g) N2(g) + O2(g) ; K = 2.2 × 1030

(D) 2NO2(g) N2(g) + 2O2(g) ; K = 6.71 × 1016

E-7. The equilibrium constant for a reaction A + B C + D is 1 × 10–2 at 298 K and is 2 at 273 K The

chemical process resulting in the formation of C and D is :

(C) unpredictable (D) there is no relationship between H and K

PART - II : MISCELLANEOUS QUESTIONS

COMPREHENSIONS TYPE

Comprehension # 1

Le chatelier's principle

If a system at equilibrium is subjected to a change of any one of the factors such as concentration, pressure

or temperature, the system adjusts itself in such a way as to Nulify the effect of that change

Change of pressure : If a system in equilibrium consists of gases, then the concentrations of all the

components can be altered by changing the pressure To increase the pressure on the system, the volumehas to be decreased proportionately The total number of moles per unit volume will now be more and theequilibirum will shift in the direction in which there is decrease in number of moles i.e., towards the direction

in which there can be decrease in pressure

Effect of pressure on melting point : There are two types of solids :

(a) Solids whose volume decreases on melting, e.g., ice, diamond, carborundum, magnesium nitride andquartz

Solid (higher volume) Liquid (lower volume)

The process of melting is facilitated at high pressure, thus melting point is lowered

(b) Solids whose volume increase on melting, e.g., Fe, Cu, Ag, Au, etc

Solid (lower volume) Liquid (higher volume)

In this case the process of melting become difficult at high pressure; thus melting point becomes high

(c) Solubility of substances : When solid substance are dissolved in water, either heat is evolved (exothermic)

or heat is absorbed (endothermic)

KCl + aq KCl(aq) – heat

In such cases, solubility increase with increase in temperature Consider the case of KOH; when this isdissolved, heat is evolved

KOH + aq KOH(aq) + heat

In such cases, solubility decrease with increase in temperature

(d) Solubility of gases in liquids : When a gas dissolves in liquid, there is decrease in volume Thus,

increase of pressure will favour the dissolution of gas in liquid

1. A gas 'X' when dissolved in water heat is evolved Then solublity of 'X' will increase :

(A) Low pressure, high temperature (B) Low pressure, low temperature

(C) high pressure, high temperature (D) high pressure, low temperature

2. Au(s) Au()

Above equilibrium is favoured at :

(A) High pressure low temperature (B) High pressure high temperature

(C) Low pressure, high temperature (D) Low pressure, low temperature

3. For the reaction,

If pressure is increased by reducing the volume of the container then :

(A) Total pressure at equilibrium will change

(B) Concentration of all the component at equilibrium will change

(C) Concentration of all the component at equilibrium will remain same

(D) Equilibrium will shift in the forward direction

Comprehension # 2

Effect of temperature on the equilibrium process is analysed by using the thermodynamics

From the thermodynamics relation

Gº = – 2.30 RT logk (1) Gº : Standard free energy change

Gº = Hº – TSº (2) Hº : Standard heat of the reaction

From (1) & (2)

– 2.3 RT logk = Hº – TSº Sº : Standard entropy change

R3.2

º

SRT3.2

If at temp T1 equilibrium constant be k1 and at temperature T2 equilibrium constant be k2 then :

The above equation reduces to:

 logK1 =

R3.2

º

STR3.2

º

H1

º

STR3.2

º

H2

2

T

1T

1R30.2

º

HK

KlogFrom the above relation we can conclude that the value of equilibrium constant increases with increase intemperature for endothermic reaction but value of equilibrium constant decreases with the increase intemperature for exothermic reaction

4. If standard heat of dissociation of PCl5 is 230 cal then slope of the graph of logk vs

7. Which is the most effective drying agent at 0°C?

(A) SrCl2 2H2O (B) Na2HPO47 H2O (C) Na2SO4 (D) all equally

8. At what relative humidities will Na2SO410 H2O be efflorescent (release moisture) when exposed to air at

0°C?

(A) above 33.33% (B) below 33.33 % (C) above 66.66% (D) below 66.66%

9. At what relative humidities will Na2SO4 be deliquescent (i.e absorb moisture) when exposed to the air at

1 mol of H2 and 3 mol of I2 gave rise at equilibrium to x mol of HI

Addition of a further 2 mol of H2 gave an additional x mol of HI What is x?

11. In above problem, what is Kp at the temperature of the experiment

12. In a study of equilibrium

2SO2(g) + O2(g) 2SO3(g)

Starting with 2 mole SO2 and 1.5 mole O2 in 5 litre flask Equilibrium mixture required 0.4 mole KMnO4 inacidic medium Hence KC is :

MATCH THE COLUMN

13. Match the following

(A) a-Q, b-P, c-P, d-R (B) a-P, b-P, c-Q, d-R (C) a-Q, b-R, c-P, d-R (D) a-R, b-P, c-P, d-Q

14. Match the following

(A) a-R, b-P, c-S, d-Q (B) a-P,R, b-P,Q, c-P, d-P,Q

15. Match the following

16. Match the following ; D - Vapour Density before Dissociation

d - Vapour Density after Dissociation

(A) a-Q, b-P, c-R, d-S (B) a-P, b-Q, c-R, d-S

17. Match List I with List II

(P is partial pressure of prdouct having stiochiometric coefficient unity)

(B) Introduction of inert gas at (Q) PCl5 (g)  PCl3 (g) + Cl2 (g)

constant pressure will decreasethe concentration of reactants(C) Kp is dimensionless (R) 2NO2 (g)  N2O4 (g)

(D) Temperature increase will shift (S) NH3 (g) + HI (g)  NH4I (s)

the reaction on product side

19. Match the following

(A) N2(g) + 3H2(g) 2NH3(g) (t = 300ºC) (p) ng > 0

(B) PCl5(g) PCl3(g) + Cl2(g) (t = 50ºC) (q) Kp < Kc

(C) C(s) + H2O(g) CO(g) + H2(g) (r) Kp not defined

(D) CH3COOH() + C2H3OH () CH3COOC2H5() + H2O() (s) Pinitial > Peq.

(A) For the equilibrium NH4(s) NH3(g) + H(g), (p) Forward shift

if pressure is increased at equilibrium(B) For the equilibrium N2(g)+ 3H2(g) 2NH3(g) (q) No change

volume is increased at equilibrium(C) For the equilibrium H2O(g) + CO(g) H2(g) + CO2 (g) (r) Backward shift

inert gas is added at constant pressure at equilibrium(D) For the equilibrium PCl5 PCl3 + Cl2 (s) Final pressure is more than

Cl2 is removed at equilibrium initial pressure

ASSERTION / REASONING

DIRECTION :

Each question has 5 choices (A), (B), (C), (D) and (E) out of which ONLY ONE is correct.

(A) Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1.(B) Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1.(C) Statement-1 is True, Statement-2 is False

(D) Statement-1 is False, Statement-2 is True

(E) Statement-1 and Statement-2 both are False

21 Statement - 1 For the reaction H2(g) + 2(g) 2H(g), Kp = Kc

Statement - 2 Kp of all gaseous reactions is equal to Kc

22 Statement - 2 Kp is related to Kc by the relation, Kp = Kc (RT) n

Statement - 2 Kp has same units as Kc

Statement - 2 If a catalyst is added to the reaction at equilibrium, the value of Q remains no

longer equal to Keq

Statement - 2 Catalyst increases the rate of forward and backward reaction to same extent.

on the reaction

Statement - 2 The reaction is not accompanied by any change in number of moles of gaseous species.

essentially constant during any reaction involving water

place in dilute aqueous solution

Statement-2 : All reversible reactions occur to reach a state of equilibrium.

expression

Statement-2 : Each pure solid or pure liquid is in a phase by itself, and has a constant concentration at

constant temperature

using any given concentrations of the species involved in the reaction, and not necessarily equilibriumconcentrations

Statement-2 : If the numerical value of Q is not the same as the value of equilibrium constant, a reaction will occur.

equation is multiplied by 2, the equilibrium constant is squared

Statement-2 : The numerical value of an equilibrium constant depends on the way the equation for the

reaction is written

solid CaCO3 is placed in an evacuated vessel enclosed by a piston and heated so that a portion of itsdecomposes If the piston is moved so that the volume of the vessel is doubled, while the temperature is heldconstant, the number of moles of CO2 in the vessel increase

Statement-2 : Catalysts influence the rate of both forward and backward reactions equally.

direction hence equilibrium constant will decrease

Statement-2 : Addition of inert gas to the equilibrium mixture at constant volume, does not alter the equilibrium.

TRUE / FALSE

34. A catalyst does not alter the equilibrium point

35. For the equilibrium, H2 + I2 2HI, the value of equilibrium constant increases with increase in

concentration of H2

36. For any reaction greater the value of equilibrium constant greater is the extent of completion of reaction

37. For the reaction, N2O4 2NO2, Kc = Kp/RT

38. For the reaction PCl5 PCl3 + Cl2, the degree of dissociation of PCl5 increases with increase in

pressure

39. The value of equilibrium constant does not depend upon pressure

40. When a liquid and its vapour are at equilibrium and the pressure is suddenly decreased, cooling occurs

41. If equilibrium constant for the reaction, A2 + B2 2AB, is K, then for the backward reaction

AB

2

1

A2 + 2

1

B2, the equilibrium constant is

K

1

42. Catalyst makes a reaction more exothermic

43. For the reaction, CaCO3(s) CaO(s) + CO2(g), Kp = PCO

2

44. A catalyst increases the value of the equilibrium constant for a reaction

45. In case of endothermic reactions, the equilibrium shifts in backward direaction on increasing the temperature

46. The value of K increases with increases in pressure

47. For the reaction, H2 + I2 2HI, the equilibrium constant, K is dimenstionless

PART - I : MIXED OBJECTIVE

Single Choice Correct :

1. A cylinder provided with a piston has some PCl5 which is in equilibrium with PCl3 and Cl2 The system is

compressed with the help of piston Indicate the correct statement :

(A) some more PCl5 will decompose (B) the system remains unaffected

(C) PCl3 and Cl2 will combine to form PCl5 (D) explosion occurs

with a degree of dissociation ‘x’ which is very small as compared to unity The expression for Kp, in terms of

‘x’ and total pressure ‘P’ is

(A)

2

Px3

(B) 3

Px2

(C) 3

Px3

(D) 2

Px2

4. In the equilibrium SO2Cl2 SO2 + Cl2 at 2000 K and 10 atm pressure, % Cl2 = % SO2 = 40 by volume.

Then

) SO ( n

) Cl SO ( n

2

2 2

= 4

1

at equilibrium(C) Kp = 8 atm (D) n(SOCl2) = n(SO2) = n(Cl2)

5. The KC for the reaction A + B C + D is 9 If one mole of each of A and B are mixed and there

is no change in volume, the number of moles of C formed is–

6. ‘a’ moles of PCl5 undergo thermal dissociation as –

PCl5 PCl3 +Cl2, the mole fraction of PCl3 at equilibrium is 0.5 The total pressure is 2.0atmosphere The partial pressure of Cl2 at equilibrium is –

7. The equilibrium constant of the reaction A + B C + D is 10 If rate constant of forward reaction

is 203, the rate constant of backward reaction is –

8. The equilibrium constants for the reaction X2 2X at 300K and 600K are 10–8 and

10–3 respectively The reaction is –

(A) Exothermic (B) Endothermic (C) Thermo neutral (D) Slow

9. The reversible reaction

[Cu(NH3)4]2+ + SO32 – [Cu (NH3)3SO3] + NH3

is at equilibrium What would not happen if ammonia is added –

(A) [SO32 – ] would increase

(B) [Cu (NH3)3SO3] would increase

(C) The value of equilibrium constant would not change

(D) [Cu(NH3)4]2+ would increase

10. Two systems

PCl5(g) PCl3(g) + Cl2(g)and COCl2 (g) CO(g) + Cl2(g)

are simultaneously in equilibrium in a vessel at constant volume If some CO(g) is introduced in the vessel atconstant volume, then at new equilibrium the concentration of :

(A) PCl5 is greater (B) PCl3 remains unchanged

11. To the system, LaCl3(s) + H2O(g) LaClO(s) + 2HCl(g) – heat

already at equilibrium, more water vapour is added without altering T or V of the system When equilibrium isre-established, the pressure of water vapour is doubled The pressure of HCl present in the system increases

by a factor of –

12. The equilibrium constant for the reaction 2 X (g) + Y (g) 2Z (g) is 2.25 What would be

the concentration of Y at equilibrium with 2.0 moles of X and 3.0 moles of Z in one litre vessel atequilibrium–

(A) 1.0 moles (B) 2.25 moles (C) 2.0 moles (D) 4.0 moles