Final answer:
When 27.9 g of magnesium metal reacts with excess hydrochloric acid, it will produce 2.31 g of hydrogen gas.
Step-by-step explanation:
To determine the grams of hydrogen gas produced when 27.9 g of magnesium reacts with excess hydrochloric acid, we need to use the balanced chemical equation for the reaction: Mg(s) + 2 HCl(aq) → MgCl₂(aq) + H₂(g). From this equation, we can see that 1 mole of magnesium produces 1 mole of hydrogen gas. The molar mass of hydrogen gas is approximately 2.016 g/mol. Therefore, the number of moles of hydrogen gas produced can be calculated.
First, we convert the mass of magnesium to moles:
27.9 g Mg × (1 mol Mg / 24.305 g Mg) = 1.146 mol Mg
Since the ratio of magnesium to hydrogen gas is 1:1, we can determine the moles of hydrogen gas produced:
1.146 mol H₂
Finally, we convert the moles of hydrogen gas to grams:
1.146 mol H₂ × (2.016 g H₂ / 1 mol H₂) = 2.31 g H₂
Therefore, 2.31 g of hydrogen gas would be produced.