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All questions of Equilibrium - Physics for NEET Exam

Ca(HCO3)2 is strongly heated and after equilibrium is attained, temperature changed to 25° C.

Kp = 36 (pressure taken in atm)
Thus, pressure set up due to CO2 is
  • a)
    36 atm
  • b)
    18 atm
  • c)
    12 atm
  • d)
    6 atm
Correct answer is 'D'. Can you explain this answer?

Mira Joshi answered
The reaction is as follow:-
Ca(HCO3)2(s)⇌CaO(s) + 2CO2 (g) + H2O(g)
At 25° C H2O goes in liquid state
Kp = (PCaO)1×(PCO2)2
(PCa(HCO3)2)
Since, Ca(HCO3)2, CaO and H2O are not in gaseous state, so their partial pressure is taken 1.
Putting all values, we have
36 = (PCO2)2 
Or PCO2 = 6 atm

Following equilibrium is set up at 298 K in a 1 L flask.

If one starts with 2 moles of A and 1 mole of B, it is found that moles of B and D are equal.Thus Kc is 
  • a)
    9.0
  • b)
    15.0
  • c)
    3.0
  • d)
    0.0667
Correct answer is option 'B'. Can you explain this answer?

Sushil Kumar answered
For the equilibrium reaction:
A+2B ⇌ 2C+D
volume of flask = 1L
Initial moles of A = 2 mol
initial concentration of A=[A]i = 2 M
initial mole of B = 1 mol 
[B]i = 1 M
[A]eq = 2-x, [B]eq = 1-2x, [C]eq = x, [D]eq = 3x
Given [D]eq = 1 * 1L
= 1 M
Thus x = 1M
[A]eq = 1, [B]eq = -1, [C]eq = 1, [D] = 3
Kc = {([D]eq)3 * ([C]eq)}/{[A]eq * ([B]eq)2
= Kc = {(3)3*1}/{1*(-1)2}
= 27/1
= 27

The exothermic formaton of ClF3 is represented by the equation -
Cl2(g)+3F2(g) 2ClF3(g) ; ΔrH = -329 kJ
Which of the following will increase the quantity of ClF3 in an equilibrium mixture of Cl2, F2 and ClF3 ?
  • a)
    Removing Cl2
  • b)
    Increasing the temperature
  • c)
    Adding F2
  • d)
    Increasing the volume of the container
Correct answer is option 'C'. Can you explain this answer?

Hansa Sharma answered
The correct answer is option C
According to Le-Chatelier's Principle, if a system at equilibrium is subjected to a change of concentration pressure or temperature then the equilibrium is shifted in such a way as to nullify the effect of change.
In the given reaction, if the concentration of F2 is increased then the reaction will shift in the forward direction in order to increase the concentration of ClF3.
Hence, 
Adding F2 .

How many of the following are Lewis bases?
    Correct answer is '6'. Can you explain this answer?

    Pooja Shah answered
    Total number of compounds acting as Lewis base in the given example is 6. H+ and BF3 are electron deficient so they can't act as Lewis base while FeCl3 acts as Lewis acid so all the other compounds except these three are Lewis base.

     In which of the following reaction can equilibrium be attained
    • a)
      Reversible reaction
    • b)
      Cyclic reaction
    • c)
      Decomposition reaction
    • d)
      Irreversible reaction
    Correct answer is option 'A'. Can you explain this answer?

    Rajat Kapoor answered
    Reversible Reaction
    The common observation for any reactions when they are reacted in closed containers would not go to completion, for some given conditions like temperature and pressure.
    For all those cases, only the reactants are found to be present in the intial stages, but with the progress of reaction, the reactants concentration decreases and to that of the products increases. A stage is finally reached where there is no more change of reactants and products concentration is observed. The state where the reactants and products concentrations do not show any visible change within a given period of time is better known as the state of chemical equilibrium. 
    The reactant amount that remains unused depends upon the experimental conditions like concentration of components, temperature of the system, pressure of the system and the reaction nature.

    Following equilibrium is set up at 1000 K and 1 bar in a 5 L flask,

    At equilibrium, NO2 is 50% o f the total volume. Thus, equilibrium constant Kc is 
    • a)
      0.133
    • b)
      0.266
    • c)
      0.200
    • d)
      0.400
    Correct answer is option 'A'. Can you explain this answer?

    The correct answer is Option A.    
                    N2O4  ⇌  2NO2
    Initial            1                 0           
    Equilibrium  1−x             2x
    Total moles = 1 - x + 2x 
    NO2 is 50% of the total volume when equilibrium is set up.
    Thus, the volume fraction (at equilibrium) of NO2 = 50/100 = 0.5 = ½
    So,    2x / (1+x) = ½
         => x = ⅓
    For 1 litre;
    Kc = [NO2] / [N2O4]
        = [4*(1/9)] / [⅔]
        = 0.66; 
    For 5 litres; 
    Kc = 0.66 / 5
    = 0.133
    Thus, option A is correct.
     

    Assume following equilibria when total pressure set up in each are equal to 1 atm, and equilibrium constant (Kp) as K1; K2 and K3


    Thus,
    • a)
       K1 = K2 = K3
    • b)
      K1 < K2 < K3
    • c)
      K3 < K2 < K1
    • d)
      None of these
    Correct answer is option 'C'. Can you explain this answer?

    The correct answer is option C
    CaCO3 ​→ CaO + CO2​
    Kp​ = k1 ​= Pco2​​
    total pressure of container P
    k1​ = p
    NH4​HS → NH3 ​+ H2​S
    PNH3​​ = PH2​S ​= P0​
    P0​ + P0​ = p (total pressure)
    P0 ​= p/2
    k2​ = kp ​= [PNH3​​][PH2​s​] p24
    NH2​CoNH2 ​→ 2NH3 ​+ CO2​
    PNH3​​ = 2P0​        PCO2​ ​= P0​
    2P0​ + P0 ​= P

    In the following reaction,

    Species behaving as Bronsted-Lowry acids are
    • a)
      A,D
    • b)
      B,C
    • c)
      A,B
    • d)
      B,D
    Correct answer is option 'A'. Can you explain this answer?

    Om Desai answered
    Bronsted lowry acids are those acids which donate H+. In the reaction, A and D are giving H+. So, these both are bronsted lowry acid.

    Kc forthe decomposition of NH4HS(s) is 1.8x 10-4 at 25°C.

    If the system already contains [NH3] = 0.020 M, then when equilibrium is reached, molar concentration are
    • a)
      a
    • b)
      b
    • c)
      c
    • d)
      d
    Correct answer is option 'B'. Can you explain this answer?

    Sushil Kumar answered
     NH4HS (s)  ⇋ NH3 (g) + H2S (g)
    Initial    1                   -               -
    At eqm     1-x                 x+0.02     x
    Kc = [NH3][H2S]   (Since NH4HS is solid, we ignore it.)
    1.8×10-4    = (x+0.02)(x)
    x2+0.02x-1.8×10-4 = 0
    Applying quadratic formula; x = -0.02+√{(0.02)2-4×1.8×10-4}
    = 0.033-0.020/2 = 0.0065
    Therefore, concn of NH3 at equilibrium = x+0.020 = 0.0265
    concn of H2S at equilibrium = x = 0.0065
    So, option b is correct

    Passage I
    Solid ammonium chloride is in equilibrium with ammonia and hydrogen chloride gases

    0.980 g of solid NH4CI is taken in a closed vessel of 1 L capacity and heated to 275° C.
    Q. Percentage decomposition of the original sample is
    • a)
      24.81%
    • b)
      6.24%
    • c)
      3.12%
    • d)
      12.13%
    Correct answer is option 'D'. Can you explain this answer?

    Knowledge Hub answered
    The state of HCl is given wrong. It will be in gaseous state.
    So, the reaction be like;-
    NH4Cl(s)  ⇌  NH3(g) + HCl(g)        kp = 1.00×10-2 at 275° C
    Kp = kc(RT)2
    1.00×10-2 = kc(0.0821×548)2
    Or kc = 4.94×10-6
                              NH4Cl(s)  ⇌  NH3(g) + HCl(g)
    Initial  1                     -             -
    At eqm 1-x                  x            x 
    Kc = x2
    x = √(4.94×10-6)
    =  2.22×10-3
    Therefore, NH4Cl dissociated at eqm = 2.22×10-3 × 53.5 = 0.118
    %age decomposition = 0.118/0.980×100 = 12.13%

    Direction (Q. Nos. 21) This section contains 2 questions. when worked out will result in an integer from 0 to 9 (both inclusive)
    Q. For the equilibrium in gaseous phase in 2 L flask we start with 2 moles of SO2 and 1 mole of O2 at 3 atm, 
    When equilibrium is attained, pressure changes to 2.5 atm. Hence, equilibrium constant Kc is
      Correct answer is '4'. Can you explain this answer?

      Om Desai answered
      The correct answer is 4
      2SO2(g) + O2(g) ⇋ 2SO3
      Initial moles      2            1
      At equilibrium 2 - 2x     1 - x    2x
      Net moles at equilibrium  =  2 - 2x + 1 - x + 2x
      =(3 - x)moles
      Initial:
               moles = 3, 
          Pressure = 3 atm,
            Volume = 2L,
                   PV = nRT
                3 x 2 = 3RT  -------- 1
      At equilibrium
           Moles = 3 - x,
      Pressure = 2.5 atm
        Volume = 2L
              P‘V = n’RT ---------- 2
      Divide eqn  2 by 1

      ⇒2.5 = 3 - x
      ⇒x = 0.5

      For the equilibrium,

      at 1000 K. If at equilibrium pCO = 10 then total pressure at equilibrium is 
      • a)
        6.30 atm
      • b)
        0.63 atm
      • c)
        6.93 atm
      • d)
        69.3 atm
      Correct answer is option 'C'. Can you explain this answer?

      Lavanya Menon answered
      C(s) + CO2(g) <=========> 2CO(g)
      Kp = pCO2/pCO2
      GIven Kp = 63 and pCO = 10pCO2
      Putting the value of pCO in above equation,
      63 = 100(pCO2)2/pCO2
      Or pCO2 = 0.63
      pCO = 6.3
      Therefore, total pressure = 6.3+0.63 = 6.93 atm

      Equilibrium can be attained i
      • a)
        all types of system
      • b)
        closed system
      • c)
        open system
      • d)
        isolated system
      Correct answer is option 'B'. Can you explain this answer?

      Preeti Iyer answered
      The equilibrium state can only be reached if the chemical reaction takes place in a closed system. Otherwise, some of the products may escape, leading to the absence of a reverse reaction. (Note that in the diagrams under "Characteristics of Chemical Equilibrium," all reactions are in closed systems.)

      Can you explain the answer of this question below:

      Equilibrium reactions are found in large scale in production of

      • A:

        ammonia

      • B:

        sulfuric acid

      • C:

        lactic acid

      • D:

        both A and B

      The answer is d.

      Shreya Gupta answered
      An understanding of equilibrium is important in the chemical industry. Equilibrium reactions are involved in some of the stages in the large-scale production of ammonia, sulfuric acid and many other chemicals. 

      What is the equilibrium expression for the reaction P4(S) + 5O2(g)  P4O10(s) ?       
      [AIEEE-2004]
      • a)
        KC = [P4O10] / [P4] [O2]5
      • b)
        KC = [P4O10] / 5 [P4] [O2]
      • c)
        KC = [O2]5
      • d)
        KC = 1/ [O2]5
      Correct answer is option 'D'. Can you explain this answer?

      In the expression for equilibrium constant (Kp or Kc) species  state are not written (i.e., their molar concentrations are not taken as 1)
      P4 (s) + 5O2 (g) ⇌ P4O10 (s)
      Thus, Kc = 1/[O2]5

      At 700 K and 350 bar, a 1 : 3 mixture of N2(g) and H2(g) reacts to form an equilibrium mixture containing X (NH3)= 0.50. Assuming ideal behaviour Kp for the equilibrium reaction, 
      • a)
        2.03x 10-4
      • b)
        3.55x 10-3
      • c)
        1.02 x 10-4
      • d)
        3.1 x 10-4
      Correct answer is option 'D'. Can you explain this answer?

      Knowledge Hub answered
      The correct answer is option A
      2.03x 10-4
      The given equation is :-
       N2​(g)+3H2​(g) ⇌ 2NH3​(g)
      Initial moles : 1             3         0
      At eqm ;       (1−x)    (3−3x)   (2x)               
      (let)
      Total moles of equation
       =1 − x + 3 − 3x + 2x = (4−2x)
      Now, X(NH3​) = 
      ⇒ 2x = 2 − x
      ⇒ 3x = 2 ⇒ x = 0.66 = 
      32​
      Now, at equation, moles of N2​= 1/3, moles of NH3​ = 4/3
                   moles of H2 ​ =3 − 2 = 1

       

      PH can be kept constant with help of
      • a)
        saturated solution
      • b)
        unsaturated solution
      • c)
        buffer solution
      • d)
        super saturated solution
      Correct answer is option 'C'. Can you explain this answer?

      Nandini Iyer answered
      A buffer is an aqueous solution containing a weak acid and its conjugate base or a weak base and its conjugate acid. ... It is used to prevent any change in the pH of a solution, regardless of solute. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications.


        Correct answer is '2'. Can you explain this answer?

        Suresh Reddy answered
        The correct answer is 2
        Here
        we know [OH-][H+]=10-14 at 25 degree Celsius
        so pka+pkb=14
        hence answer is 2

        At 273 K and 1 atm, 1 L of N2O4 (g) decomposes to NO2(g)a s given,
        At equilibrium, original volume is 25% less than the existing volume. Percentage decomposition of N2O4 (g) is thus, 
        • a)
          25%
        • b)
          50%
        • c)
          66.66%
        • d)
          33.33%
        Correct answer is option 'D'. Can you explain this answer?

        Suresh Reddy answered
        Let the initial volume of N2O4 be x and initial volume of NO2 is 0
        If the degree of dissociation is a, then the final volume of N2O4 is x(1−a) and NO2 is 2ax.
        Initial
        It equilibrium
        N2O4            ⟶              2NO2
        x                                       0
        x(1−a)                               2ax
        Total initial volume =x+0=x
        Final volume =x(1−a)+2ax=x+ax=x(1+a)
        It is given that the initial volume is 25% less than the final volume
        x=0.75×(1+a)
        1+a=1.33
        a=0.33
        So %age dissociation = 33.33%

        Can you explain the answer of this question below:

        Acidic strength is in order

        • A:

          H2O < CH3COOH < HF < NH3 

        • B:

          NH3 < H2O < CH3COOH < HF 

        • C:

          HF < CH3COOH < H2O < NH3

        • D:

          H2O < NH3 < HF < CH3COOH

        The answer is b.

        Preeti Khanna answered
        When we move from left to right, electronegativity of central atom increases. Due to this nature, central atom has more tendency to break its bond with H and acquire negative charge. So, while moving from left to right, acidic strength increase.

        Consider the reaction equilibrium  2SO2(g)+O2(g)2 SO3 (g); ΔHº = -198 kJ
        On the basis of Le Chatelier's principle, the condition favourable for the forward reaction is -
        [AIEEE-2003]
        • a)
          Lowering the temperature and increasing the pressure
        • b)
          Any value of temperature and pressure
        • c)
          Lowering of temperature as well as pressure
        • d)
          Increasing temperature as well as pressure
        Correct answer is option 'A'. Can you explain this answer?

        Riya Banerjee answered
        The correct answer is option A
         
        ACCORDING TO LE CHATELIER'S PRINCIPLE
         
        TEMPERATURE
        if we increase temperature equilibrium will shift that direction which proceeds an endothermic reaction but the reaction given in question is exothermic so we have to decrease temperature to proceed forward.
         
        PRESSURE
        at equilibrium if we increase pressure equilibrium will shift that direction which has less number of moles but in given reaction products have less no. of moles than reactant that's why we increase pressure.
         

        Passage II
        A 15 L flask at 300 K contains 64.4 g of a mixture of NO2 and N2O4 in equilibrium. Given,
        Q. Kc for the above equilibrium is 
        • a)
          164.28
        • b)
           6.087x 10-3
        • c)
          0.2708
        • d)
          3.693
        Correct answer is option 'A'. Can you explain this answer?

        Pooja Shah answered
        Kp = Kc(RT)n
        Kp = 6.67 ,
        ∆n = moles of products - moles of reactants = 1-2 = -1
        R = 0.0821 L atm mol-¹K-¹
        T = 300K
        Substitute these values in the formula,
        => Kc = 6.67×0.0821×300
        Kc = 164.28.
         

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