You are given
the mass of CaH2 which is 14 grams and H2O which is 28 grams. You are required
to find the maximum volume of H2 gas at STP. The balanced chemical reaction is
CaH2 + 2H2O -> Ca(OH)2 + H2. Note that for every one mole of CaH2, 2 moles
of H2O is needed to completely react and produce Ca(OH)2 + H2. So the CaH2 and
H2O are at equal proportions. At STP, temperature is at 0°C(273K) and pressure
at 1 atm. The molar mass of CaH2 is 42 grams per mole.
14g CaH2(1mol
CaH2/42 grams CaH2)(1mol H2/1mol CaH2) = 0.333 moles H2
The ideal gas
equation is PV=nRT, with R(gas constant) = 0.08206 L-atm/mol-K. Get the equation
for volume, we have
V=nRT/P
V=(0.333molH2)(
0.08206 L-atm/mol-K)(273K)/1atm
V=7.47L
