Question

For the reaction $A+B\rightleftharpoons 3C$ at ${25}^{0}C$

A 3Lvessel contains 1, 2, and 4 moles of A, B, and C respectively. Predict the direction of reaction if:

a) $K_C$ for the reaction is 10
b) $K_C$ for the reaction is 15
c) $K_C$ for the reaction is 10.66

• A. a) Backward direction b) Forward direction c) At equilibrium
• B. a) Forward direction b) Backward direction c) Forward direction
• C. a) Backward direction b) Forward direction c) Back direction
• D. a) Backward direction b) Backrward direction c) At equilibrium

Answer 1

The correct option is A a) Backward direction b) Forward direction c) At equilibrium

$A+B\rightleftharpoons 3C$

Before Reaction $\left[A\right]=1/3\left[B\right]=2/3\left[C\right]=4/3$
Thus,
$Q=\frac{{\left[C\right]}^3}{\left[A\right]\left[B\right]}=\frac{4^3\times 3\times 3}{3^3\times 1\times 2}=\frac{64}{6}=10.66$
A) Since $K_C=10$, thus Q must decrease to attain $K_C$ value and thus, $\left[C\right]$ must decrease or $\left[A\right]$ and $\left[B\right]$ should increase. Thus, the reaction will occur in a backward direction.

B) Since $K_C=15$ thus Q must increase to attain $K_C$ value and thus, $\left[C\right]$ must increase or $\left[A\right]$ and $\left[B\right]$ must decrease. Thus, the reaction will occur in the forward direction.

C) $Q=K_C$ thus reaction is in equilibrium,

So. the correct option is $A$