Question

The reaction A+B gives C + D is studied in a one
litre Vessel at 250°C. The initial concentration of
A was 3n and of B was n. After equilibrium was
attained then equilibrium concentration of C was
found to be equal to equilibrium concentration of
B. What is the concentration of D at equilibrium :-
a) n/2
b) 3n-n/2
(c) n+n/2
d) n

Answer 1

Answer: a. $\frac{n}{2}$

Explanation:

The given balanced equilibrium reaction is,

                            $A+B\rightleftharpoons C+D$

Initial conc.             3n      n             0     0

At eqm. conc.    (3n-x) M   (n-x) M   (x) M   (x) M

The expression for equilibrium constant for this reaction will be,

$K_c=\frac{[C]\times [D]}{[A]\times [B]}$

$K_c=\frac{x\times x}{(3n-x)(n-x)}$

we are given : x = (n-x)

n = 2x

$x=\frac{n}{2}$

Thus the value of the equilibrium concentration of D will also be $\frac{n}{2}$

Answer 2

The concentration of d at equilibrium will be n / 2.

Option (A) is correct.

Explanation:

The initial concentrations of the reactants are given below.

                             A   +     B   ⇄      C    +     D

At time "t" = 0    3n          n            0            0

At time "t" = 0    3n - x     n - x       x             x

n − x = x → x = n / 2

i.e. [D] equation  =n / 2

Thus the concentration of d at equilibrium will be n / 2.

Also learn more

What is the equilibrium concentration of each of the substances in the equilibrium when the initial concentration of ICl was 0.78 M?

2 ICl(g)⇌I2(g) + Cl2(g) ; KC = 0.14

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