Question

Cavendish prepared hydrogen in 1766 by the novel method of passing steam through a red-hot gun barrel:
4 H2O (g) + 3 Fe (s) --> Fe3O4 (s) + 4 H2 (g)

(a) Outline the steps necessary to answer the following question: What volume of H2 at a pressure of 745 torr and a temperature of 20 °C can be prepared from the reaction of 15.O g of H2O?
(b) Answer the question.

Answer 1

a)
step 1:
convert mass of H2O to mol

step 2:
use given chemical equation to calculate moles of H2 produced

step 3:
use ideal gas equation to calculate volume

b)
step 1:
convert mass of H2O to mol
mol of H2O = mass / molar mass
= 15.0/18.0
=0.833 mol

step 2:
use given chemical equation to calculate moles of H2 produced
from given equation, 4 mol of H2 is formed from 4 mol of H2O
So,
moles of H2 = moles of H2O
= 0.833 mol

step 3:
use ideal gas equation to calculate volume
use:
P*V = n*R*T
(745/760) atm * V = 0.833 mol * 0.0821 atm.L/mol.K * (20+273) K
0.9803 * V = 0.833 * 0.0821*293
V = 20.4 L

Answer: 20.4 L