What is the maximum mass of S8 that can be produced by combining 79.0 g of each reactant? 8SO2+16H2S⟶3S8+16H2O

Answer 1

Hi Ashton,

The first step is to figure out what the limiting reagent is. This is because, when we allow 79 g of each of these reagents (SO₂ and H₂S) to react, one of them will eventually run out before the other, and at that point our reaction will not make more product. The limiting reagent is the one that runs out or "depletes" first.

To find the limiting reagent, start by converting each mass of reagent to the number of moles, using the molar mass of each compound:

79.0 g SO₂ * (1 mol SO₂/64.066 g SO₂) = 1.23 mol SO₂

79.0 g H₂S * (1 mol H₂S/34.1 g H₂S) = 2.32 mol H₂S

Now, we compare the ratio of these molar quantities to the ideal stoichiometric ratio, which is given in the reaction equation (8 moles of SO₂ for every 16 moles of H₂S , which is a ratio of 8 : 16 or simplified to 1 : 2)

we have 1.23 mol SO₂ : 2.32 mol H₂S

let us simplify this ratio to make the comparison easier:

dividing both sides of this ratio by 1.23, we get 1 mol SO₂ : 1.89 mol H₂S

Comparing our above calculated ratio to the ideal 1:2 ratio given by the reaction equation, we see we have slightly less H₂S than what the chemical "recipe" calls for (1.89 is less than 2). This means that H₂S will be our limiting reagent

Now, we can finally calculate the final mass of S₈ produced. We have to base this calculation off of the starting amount of H₂S, because as we just figured out, this is our limiting reagent.

79.0 g H₂S * (1 mol H₂S / 34.1 g H₂S) * (3 mol S₈ / 16 mol H₂S) = 0.434 mol S₈

Now, convert this molar quantity of S₈ to a mass:

0.434 mol S₈ * (256 g S₈ / 1 mol S₈) = 111 grams S₈

If you are having difficulty understanding limiting reagents, here is an analogy: Let's say that you are making sandwiches, and one sandwich requires 2 bread slices and 1 patty. Now let's say you are given 1,000 bread slices and 100 patties. In this example, we will only be able to make 100 sandwiches, and we will have 800 bread slices left over (200 bread slices used). Our patties were the "limiting reagent" because we ran out of them before we ran out of bread slices.