Question

At a certain temperature, the reaction 2NO + Cl2 ⇌ 2NOCl has an equilibrium constant Kc of 45.0. A chemist creates a mixture with the following initial concentrations: [NO] = 0.10 M, [Cl2] = 0.20 M, and [NOCl] = 0.30 M. What will happen as the reaction begins?

Answer 1

This is an incomplete question, here is a complete question.

At a certain temperature, the reaction $2NO(g)+Cl_2(g)\rightarrow 2NOCl(g)$  has an equilibrium constant Kc of 45.0. A chemist creates a mixture with the following initial concentrations: [NO] = 0.10 M, [Cl₂] = 0.20 M, and [NOCl] = 0.30 M. What will happen as the reaction begins?

A. [NOCl] will increase.

B. [NOCl] will decrease.

C. [NOCl] will stay the same.

D. There is not enough information to answer the question.

Answer : The correct option is, (C) [NOCl] will stay the same.

Explanation :

Reaction quotient (Q) : It is defined as the measurement of the relative amounts of products and reactants present during a reaction at a particular time.

The given balanced chemical reaction is,

$2NO(g)+Cl_2(g)\rightarrow 2NOCl(g)$

The expression for reaction quotient will be :

$Q=\frac{[NOCl]^2}{[NO]^2[Cl_2]}$

In this expression, only gaseous or aqueous states are includes and pure liquid or solid states are omitted.

Now put all the given values in this expression, we get

$Q=\frac{(0.30)^2}{(0.10)^2\times (0.20)}=45$

The given equilibrium constant value is, $K_c=45$

Equilibrium constant : It is defined as the equilibrium constant. It is defined as the ratio of concentration of products to the concentration of reactants.

There are 3 conditions:

When $Q>K_c$ that means product > reactant. So, the reaction is reactant favored.

When $Q$ that means reactant > product. So, the reaction is product favored.

When $Q=K_c$ that means product = reactant. So, the reaction is in equilibrium.

From the above we conclude that, the $Q=K_c$ that means product = reactant. So, the reaction is in equilibrium that means the concentration of NOCl will stay the same.

Hence, the correct option is, (C) [NOCl] will stay the same.