0.80 mol/L of A and B are mixed. They react very slowly to produce C and D as follows:

A(aq) + B(aq) ⇔ C(aq) + 2D(aq)
When equilibrium is attained, the concentration of C is 0.60 mol/L and the concentration of A is:
a) 0.20 M
b) 0.40 M
c) 0.60 M
d) 0.80 M

2 answers

.......A + B ==> C + D
I.....0.8..0.8...0...0
C.....-x...-x....x...x
E...0.8-x.0.8-x..x...x

So C = x = 0.6. and
0.8-x = A = ?
0.2