Hydrogen gas can be produced from the reaction of calcium hydride and water. How many grams of calcium hydride are needed to produce 2.5 l of hydrogen gas, collected over water at 26 degrees celcius and 760 torr

2.144 g of calcium hydride are needed to produce 2.5 l of hydrogen gas, collected over water at 26 degrees celcius and 760 torr.

Explanation:

The reaction of Calcium hydride and water is given by

CaH₂ + 2H₂O > Ca(OH)₂ + 2H₂

2 moles of Hydrogen gas are produced from 1 mole of Calcium hydride.

But we need to find out how much moles of Hydrogen are produced from this reaction first.

Using the ideal gas, equation,

PV = nRT

P = pressure = 760 torr = 101325 Pa

V = volume of hydrogen gas produced = 2.5 L = 0.0025 m³

n = number of moles of Hydrogen gas produced = ?

R = molar gas constant = 8.314 J/mol.K

T = absolute temperature in Kelvin = 26°C = 299.15 K

n = PV/RT = (101325×0.0025)/(8.314×299.15) = 0.102 moles

Back to the stoichiometric balance of the reaction

CaH₂ + 2H₂O > Ca(OH)₂ + 2H₂

2 moles of Hydrogen are produced from 1 mole of Calcium hydride

0.102 moles of Hydrogen will be produced from (0.102 × 1/2) moles of Calcium hydride.

Moles of Calcium hydride = 0.051 moles.

Mass of Calcium hydride that reacted = number of moles of Calcium hydride that reacted × Molar mass

Moles mass of Calcium hydride = 42.094 g/mol

Mass of Calcium hydride that reacted = 0.051 × 42.094 = 2.144g