An inorganic chemist who studies the reactions of phosphorus halides mixes 0.105
ID: 899147 • Letter: A
Question
An inorganic chemist who studies the reactions of phosphorus halides mixes 0.105 mol of PCl5 with 0.045 mol of Cl2 and 0.045 mol of PCl3 in a 500-mL flask at 250oC . The reaction equation is PCl5(g) PCl3(g) + Cl2(g) The equilibrium constant for the reaction Kc = 4.2 x 10-2
a) Calculate the reaction quotient Q and determine whether the reaction proceeds in the forward or reverse direction. Show your calculations!
b) At equilibrium the concentration for PCl5, [PCl5]eq = 0.2065 mol/L. Calculate [PCl3]eq and [Cl2]eq
c) Calculate Kp for this reaction at 250oC.
Explanation / Answer
Reaction coefficient Q for the reaction is = [PCl3][Cl2]/[PCl5]
concentrations
PCl5= 0.105/0.5 moles/L =0.21 M , PCl3= 0.045/0.5 moles/liter =0.09M and Cl2= 0.045/0.5 mole/liter =0.09M
Q = [0.09]*[0.09]/0.21 =0.038571
This is less than the equilibrium constant of 4.2X10-2 hence the reaction proceeds in the forward direction..
From Kc= [PC3][Cl2]/[PCl5]
x= concenttation rise in PCl3 and Cl2
At equilibbrium [PCl3] =0.09+x
(0.09+x)2/0.2065 =4.2X10-2
(0.09+x)2=4.2*10-2*0.2065=0.008673
x= sqrt(0.008673)=0.093129-0.09 =0.003129
At equilibrium [PCl3] =0.003129+0.09= 0.093129 = [Cl2]
Kp= Kc(RT)deln
=4.2X10-2(0.08206*(25+273.15)=1.02758