# Chem: Equilibrium Constant Question

• BioBabe91
In summary, the given conversation discusses the equilibrium PCl5 <---> PCl3 + Cl2 and its equilibrium constant, Keq = 4.16e-2. The equilibrium concentrations are given as 1.0 M for PCl5 and 0.204 M for both PCl3 and Cl2. When the volume of the closed system is doubled, the equilibrium will shift to the right to reach a new equilibrium. Solving for the new concentrations requires using 0.5-x and 0.102+x as the concentrations for PCl5 and PCl3/Cl2 respectively. This takes into account the halving of the initial concentration and the shift in equilibrium.
BioBabe91

## Homework Statement

For the equilibrium PCl5 <---> PCl3 + Cl2, all gases, Keq = 4.16e-2. The equilibrium concentration of PCl5 is 1.0 M, and both PCl3 and Cl2 are 0.204 M. If the volume of this closed system is doubled, what are the concentrations of each gas when a new equilibrium is reached?

## Homework Equations

Keq = ([product 1]^n * [product 2]^n) / ([reactant 1]^n * [reactant 2]^n)

## The Attempt at a Solution

old E: 1 M, 0.204 M, 0.204 M
new E: PCl5: 1-x, PCl3: 0.204+x, Cl2: 0.204+x
since the equilibrium would shift to the right where there's more moles.
Now, when I try to solve it, I run into an obstacle:
4.16e-2 = ((0.204+x)(0.204+x))/(1-x)
4.16e-2 - 4.16e-2(x) = 0.0416+0.408x+x^2
0 = x^2 + 0.4496x
0 = x(x+0.4496)
But x cannot be negative!

The volume doubles for for the new E you'd have to use 0.5-x and 0.102+x as your concentrations.

Ooh that makes sense now... so the initial concentration is halved AND the equilibrium shifts.
Would have never figured that out. Thanks.

Last edited:

## 1. What is an equilibrium constant in chemistry?

An equilibrium constant is a numerical value that represents the ratio of concentrations of products and reactants at equilibrium in a chemical reaction. It is a measure of how far a reaction proceeds and is used to determine the direction and extent of a reaction.

## 2. How is the equilibrium constant calculated?

The equilibrium constant, denoted as K, is calculated by dividing the concentration of products by the concentration of reactants, with each concentration raised to the power of its respective stoichiometric coefficient. The concentrations used in the calculation must be at equilibrium and in units of molarity (M).

## 3. What factors influence the value of the equilibrium constant?

The value of the equilibrium constant is primarily influenced by temperature, pressure, and the nature of the reactants and products involved in the reaction. Changes in these factors can lead to changes in the value of K and therefore affect the direction and extent of the reaction.

## 4. How does an equilibrium constant relate to the position of equilibrium?

The value of the equilibrium constant can be used to predict the position of equilibrium in a chemical reaction. If K is large, it indicates that the reaction favors the formation of products and the equilibrium lies to the right. If K is small, it indicates that the reaction favors the reactants and the equilibrium lies to the left.

## 5. Can the equilibrium constant change?

The value of the equilibrium constant is constant for a specific reaction at a given temperature. However, changing the temperature or other factors that influence the value of K can cause it to change. Additionally, the equilibrium constant may be affected by the addition or removal of reactants or products from the reaction mixture.

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