In the context of having an opportunity they mean the same thing. You can say "I have an opportunity to leave" or "I have a chance to leave". Both of those sentences mean the same thing. However chance can also refer to probability: "There is a good chance that I will leave" or "The chances are high that I will leave" for example. Hope this helps.

An "opportunity" is always positive. It is always a good thing. It is something new. A favorable possibility has just opened up, it wasn't there before. It requires action on your part: you just "seize" or "grasp" the opportunity. There is good luck in the opportunity opening up just when you needed it. If you "seize the opportunity," there is an element of chance as to whether you will succeed or fail. Thus: "A new business has just opened up. I see a 'Help Wanted' sign in the window. This is an opportunity for me to get a job. I have to seize the opportunity by going in and applying for the job. I may get the job or not." "Chance" just means the element of luck, uncertainty, or probability. "If I apply for the job, I have a chance of getting it."