Question

Calcium hydride, CaH2, reacts with water to form hydrogen gas. CaH2(s) + 2 H2O(l) Ca(OH)2(aq) + 2 H2(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 16.0 L of H2 gas if the pressure of H2 is 740. torr at 24°C?

Answer 1

CaH2(s) + 2 H2O(l) ---------------->Ca(OH)2(aq) + 2 H2(g)

PV = nRT

V = 16L

P = 740/760   = 0.974 atm

T = 24+273 = 297K

n = PV/RT

     = 0.974*16/0.0821*297   = 0.64 moles

from balanced equation

2 moles of H2 produced from 1 mole of CaH2

0.64 moles of H2 produced from = 1*0.64/2 = 0.32moles of CaH2

mass of CaH2 = no of moles * gram molar mass

                          = 0.32*42   = 13.44g of CaH2