I'm sorry if this is somehow inappropriate to ask but I've found a rather strange question on my text book that asks "Why does the rate of dissociation of $\ce{PCl5}$ increase in the presence of $\ce{Cl2}$ ?".
Somehow I couldn't find any relevant answer to this question, which led me to possibly believe that this might be a printing mistake. But nonetheless I wanted to ask if this particular case is an exception or not.