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Chemistry Help Please!

The reversible chemical reaction: A+B<->C+D has the following equilibrium constant: Kc=[C][D]/[A][B]=4.1.
(a) Initially, only A and B are present, each at 2.00 M. What is the final concentration of A once equilibrium is reached?
(b) What is the final concentration of D at equilibrium if the initial concentrations are [A]=1.00M and [B]=2.00M?
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1 Answer

Set up an ICE table.
                 A      +      B      →      C   +      D
Initial         2.00         2.00
Change         -x            -x           +x          +x
Equil          2.00-x       2.00-x        x            x
Then K = 4.1 = x2 / (2.00 - x)2
You can solve this one by taking the square root of each side.
2.02 = (4.1)1/2 = x / (2.00 - x)
Then solve for x.   [A] = 2.00 - x
Basically this one is the same, except for the starting amounts, and you need to use the quadratic formula to solve for x.  Then, [D] = x.