In the equation below, suppose 11 grams of Zinc (Zn) react with 12 grams of Hydrogen Chloride (2HCl) to form 16 grams of Zinc Chloride (ZnCl2) and an unknown amount of Hydrogen gas (H2).

Question

Zn + 2HCl → ZnCl2 + H2

Based on the Law of Conservation of Mass, how many grams of hydrogen gas will form?

Answer 1

convert the mass to moles.
Each mole of Zn requires 2 moles of HCl.

So, determine which reagent will run out first. That will tell you how many moles of products get formed.

Each mole of Zn used produces 1 mole of H2. Convert that back to grams.

Answer 2

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