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 CaH2are needed to generate 48.0 L of H2gas at a pressure of 0.888 atm and a temperature of 32°C?

Answer 1

1st find the mol of H2 produced

Given:

P = 0.888 atm

V = 48.0 L

T = 32.0 oC

= (32.0+273) K

= 305 K

find number of moles using:

P * V = n*R*T

0.888 atm * 48 L = n * 0.0821 atm.L/mol.K * 305 K

n = 1.702 mol

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

From balanced reaction above,

mol of CaH2 produced = (1/2)*moles of H2 produced

= (1/2)*1.702 mol

= 0.851 mol

Molar mass of CaH2,

MM = 1*MM(Ca) + 2*MM(H)

= 1*40 + 2*1

= 42 g/mol

mass of CaH2,

m = number of mol * molar mass

= 0.851*42

= 35.7 g

Answer: 35.7 g