[hhs997620]

Question: PCl5(g)<->PCl3(g)+Cl2(g)
If PCl5 is 48.5% dissoicated at 473K,1ATM and 97% dissoicated at 573K, 1atm. calculate the heat of reaction for the dissociation of PCl5.

I have work out the answer by using the van't Hoff equation
ln(K2/K1) = dH/R(1/T1 - 1/T2)
However, by substituting Kc(equilibrium constant of concentration) into the equation, the result is +90.98kJ/mol; while substituting Kp(equilibrium constant of partial pressure) into the equation, the result is +95.3kJ/mol.(N.B. I worked out the Kc and Kp by myself and it is not provided in the question.)
So, whether Kp or Kc should be used in the calculation?
If both of them are applicable, could anyone show me how to work out the question.
P.S. the answer of this question is +90.98kJ/mol