Question #d54a2

1 Answer
Dec 11, 2017


#"0.250 moles"#


The balanced chemical equation basically tells you how many moles of each chemical species involved in the reaction will be consumed or produced relative to each other.

In this case, you have

#"Mg"_ ((s)) + 2"HCl"_ ((aq)) -> "MgCl"_ (2(aq)) + "H"_ (2(g)) uarr#

The #2# added in front of the hydrochloric acid tells you that the reaction will always consume twice as many moles of hydrochloric acid than moles of magnesium metal.

Moreover, the balanced chemical equation tells you that for every mole of hydrochloric acid consumed by the reaction, you get #1# mole of magnesium chloride and #1# mole of hydrogen gas.

In your case, #0.500# moles of hydrochloric acid are said to react, so the reaction will produce

#0.500 color(red)(cancel(color(black)("moles HCl"))) * "1 mole H"_2/(2color(red)(cancel(color(black)("moles HCl")))) = "0.250 moles H"_2#

The answer is rounded to three sig figs.