If O2 Was The Excess Reagent 8.3 Mol
To solve a problem like this, look at the coefficients of the balanced chemical equation. In this case, it tells you that for every two moles of H2S you react, you will produce two moles of HOH. That assumes a 100% yield.
In the given problem, since you started with 8.3 moles of H2S, you would expect 8.3 moles of HOH at 100% yield.
In your case, you produced 137.1 g of water. Convert this to moles which means divide 137.1 by the formula mass of water (18.016 g/mole) .
137.1 g/ 18.016 g/mole = 7.61 moles of water.
To find % yield, divide the actual yield by the theoretical yield and multiply by 100.
% yield = 7.61/8.3 * 100 = 91.69%
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