4Ga + 3S2 ⇒ 2Ga2S3 How many moles of Sulfur are needed to react with 100.0 grams of Gallium?

1.076 mol (corrected to 2 d.p.)

Explanation:

Take the atomic mass of Ga be 69.7.

since no. of moles = mass/ molar mass,

no. of moles of Ga used = 100.0 / 69.7

= 1.43472023 mol

From the balanced equation, the mole ratio of Ga:S2 = 4:3, which means every 4 moles of  Ga can react completely with 3 moles of S2.

So, let the no. of moles of Sulphur required be y.

4 y =  1.43472023 x 3

y = 1.076 mol (corrected to 2 d.p.)