While chance and risk both refer to events that are uncertain, the usage of the words is in different contexts. The word "chance" is used when referring to positive things and "risk" when referring to negative things. For example, "chance of survival", "risk of failure".
"Chance vs Risk." Diffen.com. Diffen LLC, n.d. Web. 23 Jul 2014. < http://www.diffen.com/difference/Chance_vs_Risk >