Question #85af7

1 Answer
Feb 24, 2015

First things first, your equation is mistyped, since you have oxygen on the reactans' side, but not on the products' side. The correct balanced equation for this reaction is this one

8H_(2(g)) + S_(8(g)) -> 8H_2S_((g))

Now for the mole ratio between H_2 and H_2S. What a mole ratio tells is in what proportion the two compounds will be when this reaction takes place. Notice that the coefficients in front of H_2 and H_2S are both equal to 8.

This is what a "1:1" mole ratio is - the number of moles of one compounds is identical to the number of moles of another compound.

What that means is that regardless of how many moles of H_2 you have, the number of moles of H_2S produced will always be equal to the number of moles of H_2 that react.

If you have, for example, 0.100 moles of H_2 that react, you'll automatically have 0.100 moles of H_2S that are produced.

By comparison, the mole ratio between H_2 and S_8 is "8:1". Regardless of how many moles of S_8 react, you'll always have 8 times more moles of H_2 that are needed to react.

In essence, a mole ratio tells you the proportion in which the species involved in a reaction must be at all times.

So, if I give you 0.0250 moles of H_2 and ask you to tell me the number of moles of S_8 you need to react with this amount of hydrogen and the number of moles of H_2S you produce, use the mole ratios.

"0.0250 moles"H_2 * ("1 mole"S_8)/("8 moles"H_2) = "0.00313 moles" S_8

"0.0250 moles"H_2 * ("1 mole"H_2)/("1 mole"H_2S) = "0.0250 moles" H_2S