Question

Zn + HCl --> ZnCl2 + H2
If 18 grams of Zn are used in the following reaction, how many grams of H2 will be produced?

Answer 1

first let's see if the chemical equation is balanced.
Zn + HCl --> ZnCl2 + H2
since not yet balanced, then we balance it :P
Zn + 2HCl --> ZnCl2 + H2
since we are given grams of Zinc, we need to find the mass of Zn from periodic table to convert it to moles. thus
Zn = 65.4 g/mol
also since we are required to find grams of H2, we look also for the mass of H:
H = 1 , thus
H2 = 1*2 = 2 g/mol
therefore,
18 g Zn * (1 mol Zn / 65.4 g Zn) * (1 mol H2 / 1 mol Zn) * (2 g H2 / 1 mol H2) = 0.55 g H2

hope this helps~ :)