Question

Calcium hydride (CaH₂) reacts with water to form hydrogen gas:

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

How many grams of CaH₂ are needed to generate 55.0 L of H₂ gas at a pressure of 0.811 atm and a temperature of 32°C?

Answer 1

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

42g...............................................2x22.4L (STP condition)

?.................................................55L

=55x42/2x22.4

=51.562 g.

According to the question

P=0.81 atm, Temperature(T) = 32⁰C

According to the Ideal gass equation PV =nRT

PV/nT = R, V is constant (56 L).

n= no of moles . n= wt/molecular weight

molecular weight is constant.

P₁/w₁xT₁ =P₂/w₂ x T₂

P1 = 1 atm (STP ), T1 = 273K (STP), w₁ = 51.562 g (caluculated).

P2 = 0.81 atm , T1 = 32+273 K = 305K w₂ =?

1/51.562 x 273 = 0.81/305 x w₂

w2 = 51.562 x 273 x 0.814/305

w2 = 37.383 g.