Question

2 moles PCl5 are heated in a 2L flask.At equilibrium 40% PCl5 dissociates . what is the equilibrium constant for this reaction?

Answer 1

`K_c = 0.27`

Explanation:

THE GIVEN REVERSIBLE GASEOUS REACTION & ICE TABLE

`" "PCl_5(g)" "rightleftharpoons" "PCl_3(g)" "+" "Cl_2(g)`

I `" "2" mol"" "" "" "" "0 " mol"" "" "" "" "0" mol"`

C `-2alpha" mol"" "" "" "" "2alpha " mol" " "" "" "2alpha" mol"`

E `" "2(1-alpha)" mol"" "2alpha" mol"" "" "" "2alpha" " "mol"`

`"Where degree of dissociation, "alpha=40%=0.4`

`"Volume of the equilibrium mixture, V = 2 L"`

At equilibrium the molar concentrations of the components of the mixture are

`[PCl_5(g) ] =(2(1-alpha))/V=(2(1-0.4))/2= "0.6 mol·L"^-1`

`[PCl_3(g) ]=(2(alpha))/V=(2xx0.4)/2= "0.4 mol·L"^-1`

`[Cl_2(g) ]=(2(alpha))/V=(2xx0.4)/2="0.4 mol·L"^-1`

Equilibrium constant

`" "K_c=([PCl_3(g) ]xx[Cl_2(g) ]) /[(PCl_5(g) ) ]`

`" "=(0.4xx0.4)/0.6 " mol·L"^-1`

`" "=0.27 " mol·L"^-1`