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Mass Transfer - Engineering

Q1:

In case of an ideal solution, the total vapor pressure varies __________ with the composition expressed as mole fraction,

A inversely

B linearly

C exponentially

D none of these

ANS:B - linearly

In the case of an ideal solution, the total vapor pressure varies linearly with the composition expressed as mole fraction. This behavior is described by Raoult's law, which states that the partial vapor pressure of each component in an ideal solution is directly proportional to its mole fraction in the solution. Mathematically, this relationship can be expressed as: 𝑃total=𝑥𝐴𝑃𝐴⋆+𝑥𝐵𝑃𝐵⋆Ptotal​=xA​PA⋆​+xB​PB⋆​ Where:

  • 𝑃totalPtotal​ is the total vapor pressure of the solution,
  • 𝑥𝐴xA​ and 𝑥𝐵xB​ are the mole fractions of components A and B respectively,
  • 𝑃𝐴⋆PA⋆​ and 𝑃𝐵⋆PB⋆​ are the vapor pressures of pure components A and B respectively.
Since the total vapor pressure is the sum of the partial pressures of the components, it varies linearly with the mole fractions of the components in the solution. So, the correct answer is: linearly.