Question

If the equilibrium concentrations for $X_2,Y_2$ and $XY$ are $1.2\times {10}^{3}M,5.83\times {10}^{12}M$ and $8.9\times {10}^{2}M$ respectively, what was the initial concentration $X_2$ before the reaction occured to from $XY$?

• A. $8.83\times {10}^{-1}M$
• B. $1.65\times {10}^{3}M$
• C. $1.13\times {10}^{3}M$
• D. $2.09\times {10}^{3}M$

Answer 1

Answer: (B)

$1.65\times {10}^{3}M$

$X_2+Y_2\to 2XY$

$a_0-x+b_0-x\to 2x$

Here, $2x=8.9\times {10}^2\Rightarrow x=4.45\times {10}^{2}M$

Also, $a_0-x=1.2\times {10}^{3}M$

$\therefore a_0=(1.2\times {10}^3+4.45\times {10}^2)M=1.645\times {10}^{3}M$

$\therefore$ Initial concentration of $X_2=a_0=1.645\times {10}^{3}M$