Chance: the likelihood of something happening, based on a guess.
Usually, if the probability of an event is greater than 5%, it is considered to have a chance of happening.
e.g. there is a chance it might rain today because I see clouds in the sky.
Probability: the quantified likelihood of something happening out of all the possibilities, based on the average behaviour of the experiment in question.
e.g. there is 50% probability that you’ll get heads in the toss of an unbiased coin. It is about accurately estimating the odds of something happening.
Now by 50% chance I don’t mean that if you toss a coin twenty times you’ll get heads 10 times and tails 10 times, in fact that rarely happens. But your results will be close to 10, i.e. you might get heads 11 times and tails 9 times or, heads 8 times and tails 12 times.
Mathematically, we say that if you repeat this experiment infinite (read very large) number of times, about 50% of the times you’ll get heads. It may not be exactly 50%, but it will be close to it.