Question #fcb1b

The idea here is that when kept under constant pressure and temperature, the volume of gas is directly proportional to how many moles of gas it contains #-># this is known as Avogadro's Law.

This means that for a chemical reaction that involves gases kept under the same conditions for pressure and temperature, the mole ratios given by the stoichiometric coefficients become equivalent to volume ratios.

#color(blue)(|bar(ul(color(white)(a/a)n_1/n_2 = V_1/V_2color(white)(a/a)|))) -># the mole ratio is equivalent to a volume ratio

So, the balanced chemical equation that describes the formation of hydrogen chloride from hydrogen gas and chlorine gas looks like this

#"H"_ (2(g)) + "Cl"_ (2(g)) -> color(red)(2)"HCl"_ ((g))#

Notice that #1# mole of hydrogen gas needs #1# mole of chlorine gas to produce #color(red)(2)# moles of hydrogen chloride.

Since all the gases are kept under the same conditions for pressure and temperature, this is equivalent to saying that #"1 L"# of hydrogen gas needs #"1 L"# of chlorine gas to produce #color(red)(2)color(white)(a)"L"# of hydrogen chloride.

Since you must produce #"2 L"# of hydrogen chloride, it follows that you must consume #"1 L"# of chlorine gas, provided of course that you also have #"1 L"# of hydrogen gas available for the reaction.

#"volume of Cl"_(2(g)) = color(green)(|bar(ul(color(white)(a/a)color(black)("1 L")color(white)(a/a)|)))#