The problem states:
Calcium hydride, CaH2, reacts with water to form hydrogen gas.
CaH2(s) + 2H2O(l) Ca(OH)2(aq) + 2H2(g)
This reaction is sometimes used to inflate life rafts, weather balloons, and the like, where a simple, compact means of generating H2 is desired. How many grams of CaH2 are needed to generate 18.0 L of H2 gas if the pressure of H2 is 770 torr at 17°C?
I have no idea how to even start this problem, so could someone point me in the right direction :]