Question

A + B <=> C + 2D. One mole of A and one mole of B are placed in a .400L container. After equilibrium has been established what is the Kc?

Answer 1

*After equilibrium has been established there is .2 moles of C.

Answer 2

Using the molar ratios of the balanced equation and knowing that there are .2 moles of C AFTER equilibrium is established we know the following:
Moles of A = .2
Moles of B = .2
Moles of D = .4
I'm going to assume this is a gas. Therefore we can find the concentrations of all the species using \[mol/L =M\]
Therefore the concentrations are as follows:
A= .5
B= .5
c= .5
D = 1
Now that we know the concentrations we can make an equilibrium expression (products/ reactants)
\[Kc = \left[ A \right]\left[ B \right]/\left[ C \right]\left[ D \right]^{2}\]
Plug in the concentrations where they belong and solve for Kc
you should get Kc=.5