Q17.88CP - Chemistry: Molecular Nature Of Matter And Change

Question

An inorganic chemist places 1 mol of BrCl in container A and 0.5 mol of Br₂ and 0.5 mol of Cl₂ in container B. She seals the containers and heats them to 300⁰C. With time, both containers hold identical mixtures of BrCl, Br₂, and Cl₂.

(a) Write a balanced equation for the reaction in container A.

(b) Write the reaction quotient, Q, for this reaction.

(c) How do the values of Q in A and in B compare over time?

(d) Explain on the molecular level how it is possible for both containers to end up with identical mixtures.

Step-by-Step Solution

Answer

1. $\text{BrCl}\left(\text{g}\right)\rightleftharpoons {\text{Br}}_{\text{2}}\left(\text{g}\right){\text{ + Cl}}_{\text{2}}\left(\text{g}\right)$
   
2. Reaction Quotient, Qc : ${\text{Q}}_{\text{C}}\text{ = }\frac{\left[{\text{Br}}_{\text{2}}\right]\left[{\text{Cl}}_{\text{2}}\right]}{\left[\text{BrCl}\right]}$

c. Change in concentration will also affect Q value. As the time progress concentration decreases from its initial value and Q value also decrease.

d. Both containers are filled with exact 1 mole concentration of BrCl.

Step 1: Balanced equation

Container A is filled with 1 mol of BrCl undergoes decomposition to give Br₂ and Cl₂. The balanced equation is shown below:

$\text{BrCl}\left(\text{g}\right)\rightleftharpoons {\text{Br}}_{\text{2}}\left(\text{g}\right){\text{ + Cl}}_{\text{2}}\left(\text{g}\right)$

Step 2: Reaction quotient, Qc

Reaction quotient can be constructed by placing the concentration term of product in numerator and reactant term in denominator. 

${\mathbf{Q}}_{\mathbf{C}}\mathbf{=}\frac{\left[{\mathbf{Br}}_{\mathbf{2}}\right]\left[{\mathbf{Cl}}_{\mathbf{2}}\right]}{\left[\mathbf{BrCl}\right]}$

Step 3: Change in value of Q

As the reaction proceeds, there is a change in concentration until the system reaches the equilibrium. In the initial stage concentration of reactants is high and has Q value. After some time, there is a difference in concentration from its initial value. Also, there is a change in Q value. When the reaction reaches at equilibrium at a certain temperature it will equal to Q. 

Step 4: How identical mixtures possible

In container A 1 mole BrCl is converting to exactly half to its products such as Br₂ and Cl₂. Whereas container B holds 0.5 mol Br2 and Cl2 giving 1 mole BrCl. Thus, both containers filled with identical mixtures.