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Chapter: 11th Chemistry : Physical and Chemical Equilibrium

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Brief questions and answers: Physical and Chemical Equilibrium

Brief questions and answers: Physical and Chemical Equilibrium

26. If there is no change in concentration, why is the equilibrium state considered dynamic ?


27. For a given reaction at a particular temperature, the equilibrium constant has constant value. Is the value of Q also constant ? Explain.


28. What the relation between KP and KC. Give one example for which KP is equal to KC.


29. For a gaseous homogeneous reaction at equilibrium, number of moles of products are greater than the number of moles of reactants. Is KC is larger or smaller than KP.


30. When the numerical value of the reaction quotient (Q) is greater than the equilibrium constant (K), in which direction does the reaction proceed to reach equilibrium ?


31. For the reaction,

A2(g) + B2(g) 2AB(g) ; ΔH is –ve.

the following molecular scenes represent different reaction mixture (A – green, B – blue)

i) Calculate the equilibrium constant KP and (KC).

ii) For the reaction mixture represented  by scene (x), (y) the reaction proceed  in which directions ?

iii) What is the effect of increase in pressure  for the mixture at equilibrium.



32. State Le-Chatelier principle.


33. Consider the following reactions,

a) H2(g) + I2(g) 2 HI

b) CaCO3 (s) CaO (s) + CO2(g)

c) S(s) + 3F2 (g) SF6 (g)

In each of the above reaction find out whether you have to increase (or) decrease the volume to increase the yield of the product.


34. State law of mass action.


35. Explain how will you predict the direction of a equilibrium reaction.


36. Derive a general expression for the equilibrium constant KP and KC for the reaction

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


37.  Write a balanced chemical equation for a equilibrium reaction for which the equilibrium constant is given by expression



38. What is the effect of added inert gas on the reaction at equilibrium.


39. Derive the relation between KP and KC.


40. One mole of PCl5 is heated in one litre closed container. If 0.6 mole of chlorine is found at equilibrium, calculate the value of equilibrium constant.



41. For the reaction

SrCO3 (s) SrO (s) + CO2(g),

the value of equilibrium constant KP = 2.2 × 10–4 at 1002 K. Calculate KC for the reaction.


for the reaction,

SrCO3 (S) SrO(S) + CO2(S)

Δng = 1 – 0 = 1

KP = KC (RT)

2.2 × 10–4 = KC (0.0821) (1002)

KC = 2.2 x 10-4 / 0.0821x1002



42.  To study the decomposition of hydrogen iodide, a student fills an evacuated 3 litre flask with 0.3 mol of HI gas and allows the reaction to proceed at 500 0C. At equilibrium he found the concentration of HI which is equal to 0.05 M. Calculate KC and KP.


V = 3L

[HI]initial = 03mol/3L = 0.1 M

[HI]eq = 0.05 M

2HI(g) H2(g) + I2(g)

Kc = [H2][I2] / [HI]

= 0.025 x 0.025 / 0.05x0.05

Kc= 0.25

KP = KC (RT)Δng

Δng = 2 – 2 = 0

KP = 0.25 (RT)º

KP = 0.25


43. Oxidation of nitrogen monoxide was studied at 200 0C with initial pressures of 1 atm NO and 1 atm of O2. At equilibrium partial pressure of oxygen is found to be 0.52 atm calculate KP value.


2NO (g) + O2(g) 2NO2(g)


44. 1 mol of CH4, 1 mole of CS2 and 2 mol of H2S are 2 mol of H2 are mixed in a 500 ml flask. The equilibrium constant for the reaction KC = 4 × 10–2 mol2 lit–2. In which direction will the reaction proceed to reach equilibrium ?


CH4(g) + 2H2S(g) CS2(g) + 4H2(g)

KC = 4 × 10–2 mol lit–2

Volume = 500 ml = 1/2 L

Q > KC

The reaction will proceed in the reverse direction to reach the equilibrium.


45. At particular temperature KC = 4 × 10–2 for the reaction

H2S(g) H2(g) + ½ S2(g)

Calculate KC for each of the following reaction

i) 2H2S (g) 2H2 (g) + S2 (g)

ii) 3H2S (g) 3H2 (g) + 3/2 S2(g)



46. 28 g of Nitrogen and 6 g of hydrogen were mixed in a 1 litre closed container. At equilibrium 17g NH3 was produced. Calculate the weight of nitrogen, hydrogen at equilibrium.



mN2 = 28 g

mH2= 6g

V = 1 L


47. The equilibrium for the dissociation of XY2 is given as,

2XY2 (g) 2XY (g) + Y2(g)

if the degree of dissociation x is so small compared to one. Show that 2 KP = PX3 where P is the total pressure and KP is the dissociation equilibrium constant of XY2.



48. A sealed container was filled with 1 mol of A2 (g), 1 mol B2 (g) at 800 K and total pressure 1.00 bar. Calculate the amounts of the components in the mixture at equilibrium given that K = 1 for the reaction

A2 (g) + B2 (g) 2AB (g)



49. Deduce the Vant Hoff equation.


50. The equilibrium constant KP for the reaction

N2(g) + 3H2(g) 2NH3(g) is 8.19 × 102 at 298 K and 4.6 × 10–1 at 498 K. Calculate ΔH0 for the reaction.



 51. The partial pressure of carbon dioxide in the reaction

CaCO3 (s) CaO (s) + CO2(g) is 1.017 × 10–3 atm at 5000 C. Calculate KP at 6000c C for the reaction. ΔH for the reaction is 181 KJ mol–1 and does not change in the given range of temperature.


PCO2 = 1.017x10-3 atm T = 500º C

Kp = PCO2

KP1 = 1.017x10-3  T=500+273=773K

KP2 = ?  T=600+273=873K

∆Hº = 181KJmol-1

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