How Does Increased Pressure Affect Chemical Equilibrium in the Reaction A⇔2B?

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Discussion Overview

The discussion revolves around the effect of increased pressure on the chemical equilibrium of the reaction A⇔2B. Participants explore the implications of pressure changes on the equilibrium state, focusing on the mathematical relationships involved and the interpretation of equilibrium constants.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant states that increasing pressure will shift the reaction in the backward direction, suggesting that some moles of B will decompose to restore equilibrium.
  • Another participant corrects the initial claim about the equilibrium constant, asserting that it should be derived from pressures or concentrations rather than just moles.
  • A different participant emphasizes the need to express the equilibrium constant in terms of partial pressures and mole fractions, proposing a formula that incorporates these factors.
  • One participant questions whether they can proceed with their original method for calculating final mole fractions, indicating uncertainty about the approach.
  • Another participant expresses that there is insufficient data to solve the problem, suggesting a lack of clarity in the information provided.
  • A later reply humorously acknowledges their own role in creating the problem, indicating a light-hearted take on the confusion surrounding the discussion.

Areas of Agreement / Disagreement

Participants do not reach a consensus on how to approach the problem, with multiple competing views on the interpretation of the equilibrium constant and the effects of pressure changes. The discussion remains unresolved regarding the correct method to calculate the final mole fractions and the new equilibrium state.

Contextual Notes

Limitations include the lack of specific values for the equilibrium constant and the initial pressure, as well as the dependence on definitions of equilibrium in terms of pressures versus moles. The discussion also highlights unresolved mathematical steps in calculating the new equilibrium state.

subhradeep mahata
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Homework Statement


Consider the reaction : A⇔2B (⇔ stands for reversible). 1 mol of A and 2 mol of B are taken in a closed container at equilibrium. Suppose the pressure is increased, how much of B (by moles) will decompose to restore equilibrium ?

Homework Equations

The Attempt at a Solution


Okay, i know that reaction will be in backward direction in this case if pressure is increased.
A ⇔ 2B
Eq initial 1mol , 2mol
Eq final 1+x mol , 2-2x mol (2x mol of B decomposes to form x mol of A)
equilibrium constant = 22 / 1 = 4
it will not change with pressure
So, (2-2x)2 / 1+x = 4
x is coming out to be 3.
But if i see, at eq final the remaining moles of B is 2-2*3, -4 !
How is it possible ? Please help me rectify my mistake.
 
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subhradeep mahata said:
equilibrium constant = 22 / 1 = 4

This is not the equilibrium constant, this is just the initial reaction quotient. You need the equilibrium constant value from some other source.
 
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Even if it is at equilibrium initially, that is not the equilibrium constant. The equilibrium constant is not expressed using moles but pressures (or concentrations), and if the number of moles is not equal on both sides of the equation, pressure is a factor in the equilibrium constant. If partial pressure is P*mole fraction, then
K = (2P/3)2/(P/3) = 4P/3 where P is the initial equilibrium pressure
If P1 is the final equilibrium pressure, can you calculate the mole fractions and partial pressures (as functions of x), and an expression for the equilibrium constant?
Suppose the question is "you change the pressure to P2, and the system adjusts to a new equilibrium state." Can you find the new equilibrium pressure, then proceed as above?
 
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Yes, the value of K will be same, so 4P/3 = (mole fraction of B * P2)2 / (mole fraction of A* P2)
But i think i need some help in calculating the final mole fraction.
Shall i proceed in the same way as i did in my original attempt ?
 
There is not enough data to solve the problem.
 
Yes i too think so, as i myself made the problem ! ;-)
 

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