Question

Calcium Hydride reacts with water to produce hydrogen gas:
CaH2(s) + H2O (l)---> Ca(OH)2 (aq) + H2

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 10.0L of H2 gas if the pressure is 740mmHg are 23 degrees Celsius?

R=62.36 L.mmHg/mol.K

Answer 1

I don't know anything about this R you quote. Work it the long way.
Here's an example. Find mole H2 from PV = nRT
http://www.jiskha.com/science/chemistry/stoichiometry.html

Answer 2

CaH2 + 2H2O = Ca(OH)2 + 2H2
H2: P:.97 atm T: 296K V: 10L
PV=nRT
n=PV/RT
n= (.97*10)/(0.08206*296)
n= .40mol
.4 mol H2 (1molCaH2/2mol H2)(1mol/42g) = 8.4 g CaH2