This question is providing the equilibrium constant for the decomposition of PCl5, by the way, to PCl3 and Cl2. Thus, the equilibrium concentrations of all species are required and found to be 0.0206 M, 0.0294 M and 0.0294 M, respectively, and after doing the following equilibrium-based calculations:
In chemistry, chemical equilibrium is a condition a chemical reaction reaches when it cannot proceed anymore up to a specific extent of conversion of reactants to products.
In such a way, when having a chemical equation, one can apply the law of mass action, in order to know a constant ratio, or equilibrium expression, at which the reaction stops and maintains constant as the time goes by.
Thus, we can write the equilibrium expression for this reaction as follows:
[tex]K=\frac{[PCl_3][Cl_2]}{[PCl_5]}[/tex]
Next, we apply the ICE chart to write the aforementioned in terms of the reaction extent, x:
[tex]0.0420=\frac{x*x}{0.0500M-x}[/tex]
And thus solve for x to get the following results:
[tex]x_1=-0.0714M\\\\x_2=0.0294M[/tex]
Evidently, the correct answer is x2 because we are talking about concentrations that cannot be negative for any reason. Hence, the concentrations at equilibrium turn out to be:
[tex][PCl_3]=x=0.0294M[/tex]
[tex][Cl_2]=x=0.0294M[/tex]
[tex][PCl_5]=0.0500M-x=0.0206M[/tex]
Learn more about equilibrium expressions: https://brainly.com/question/7069485
