For the equilibrium system
`2HX(g) hArr H_(2)(g)+X_(2)(g)`
the equilibrium constant is `1.0xx10^(-5)`. What is the concentration of HX if the equilibrium concentration of `H_(2)` and `X_(2)` are `1.2xx10^(-3)` M, and `1.2xx10^(-4)` M respectively?

Options

A. `12xx10^(-4) M`
B. `12xx10^(-3) M`
C. `12xx10^(-2) M`
D. `12xx10^(-1) M`

Answer

C

Explanation

`{:(,2HX,hArr,H_(2)(g),+,X_(2)(g)),("At equilibrium",?,,1.2xx10^(-3) M,,1.2xx10^(-4) M):}`
`K=([H_(2)][X_(2)])/([HX]^(2))`
`10^(-5)=(1.2xx10^(-3)xx1.2xx10^(-4))/([HX]^(2))`
`[HX]=sqrt((1.2xx1.2xx10^(-7))/(10^(-5)))`
`=1.2xx10^(-1)`
`=12xx10^(-2) M`