[haber101]

can someone verify the answer to this question.

PCl5(g)  ⇄  PCl3(g)  +  Cl2(g)

   When a certain amount of PCl5 is heated in a 10.0 L container, an equilibrium is    established is which 0.25 moles of Cl2 is present. If Keq is equal to 0.0417, calculate the    initial number of moles of PCl5.

i get 0.039 moles

[Schrödinger]

Can you tell us how you arrived at the answer? Perhaps that way, we would be able to help you better

[haber101]

simply by using an ice table.
           PCL5 <---> PCL3+CL2
i             y              0.00 0.00
c            -x             +x     +x
e         y-0.025        0.025 0.025

an then using the equilibrium for the expression

0.0417=[0.025][0.025]/[y-0.025]

and simply solving for y, initial moles of PCL5.

[Schrödinger]

The method is correct.

But what do x and y refer to ? concentrations or moles?

[haber101]

The method is correct.

But what do x and y refer to ? concentrations or moles?

so it must be 0.39.

[FreeTheBee]

Try verifying your answer by filling it in the expression you derived to solve the problem.