What are the equilibrium partial pressures of \rm PCl_3 , \rm Cl_2, and \rm PCl_5, respectively? For the exothermic reaction PCl3(g)+Cl2(g)\rightleftharpoons PCl_5(g) K_{\rm p} = 0.100 at a certain temperature. A flask is charged with 0.500 \rm atm \rm PCl_3 , 0.500 \rm atm \rm Cl_2, and 0.300atm \rm PCl_5 at this temperature.