For the reaction N2(g) + 3H2(g) \(\rightleftharpoons\) 2NH3(g) ΔH = -ve : 

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HTET TGT Science 2020 Official Paper
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  1. Kp = Kc (RT)-2
  2. Kp = Kc
  3. Kp = Kc RT
  4. Kp = Kc (RT)-1

Answer (Detailed Solution Below)

Option 1 : Kp = Kc (RT)-2
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HTET PGT Official Computer Science Paper - 2019
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60 Questions 60 Marks 60 Mins

Detailed Solution

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Concept:

Haber's process:

  • This process is used in large scale preparations of ammonia.

N2 + 3H2 → 2NH3

  • During the process, nitrogen and hydrogen are used in the ratio 1:3.
  • The process is exothermic ΔH = -ve  in nature means heat is produced in the process.
  • According to the Le-chateliar principle, the temperature is kept high to speed up the process.
  • The gaseous ammonia produced is converted to liquid ammonia to remove the products formed.
  • This drives the reaction forward.

Equilibrium Constants:

  • The constants Kp and Kc are both equilibrium constants.
  • Kp is used when the concentration terms are given in partial pressures i.e, in gaseous reactions.
  • Kc is used when the reaction terms are expressed in molarities.
  • The relation between Kp and Kis given by:

\({K_p} = {K_c} \times {\left( {RT} \right)^{\Delta n}}\) where R = Universal gas constant, T = Temperature, and \(\triangle n\) = change in moles of gases in the reaction.

Calculation:

  • The relation between Kand Kc is

\({K_p} = {K_c} \times {\left( {RT} \right)^{\Delta n}}\)

For the reaction

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

\(No.\;of\;moles\;of\;products = 2\)

\(No.\;of\;moles\;of\;reactants = 3 + 1 = 4\)

\(Change\;in\;number\;of\;moles\;of\;gases = {n_{products}} - {n_{reactants}} = \;\Delta n\)

\( = 2 - 4 = - 2\)

Hence,

\({K_p} = {K_c} \times {\left( {RT} \right)^{-2}}\)

Hence, or the reaction N2(g) + 3H2(g) \(\rightleftharpoons\) 2NH3(g) ΔH = -ve, \({K_p} = {K_c} \times {\left( {RT} \right)^{-2}}\)

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