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NEETChemistryThermodynamics (C)

For the synthesis of ammonia by the Haber process, N ₂( g ) + 3 H ₂( g ) 2 NH ₃( g ) What is the correct relationship between the change in enthalpy ( H ) and the change in internal energy ( U ) at constant temperature?

Options

  1. AH = U + 2 RT
  2. BH = U - 2 RT
  3. CH = U - RT
  4. DH = U + RT

Correct answer

B. H = U - 2 RT

Step-by-step solution

For the given reaction: N ₂( g ) + 3 H ₂( g ) 2 NH ₃( g ) The change in the number of moles of gaseous species ( n _ g ) is calculated as: n _ g = ( moles of gaseous products ) - ( moles of gaseous reactants ) n _ g = 2 - (1 + 3) = 2 - 4 = -2 The relationship between change in enthalpy ( H ) and change in internal energy ( U ) is given by: H = U + n _ g RT Substituting the value of n _ g , we get: H = U - 2 RT Answer: H = U - 2 RT

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