Question

Silicon nitride (Si3N4), a valuable ceramic, is made by the direct combination of silicon and nitrogen at high tem- perature. How much silicon must react with excess nitro- gen to prepare 125 g silicon nitride if the yield of the reaction is 95.0%?

Answer 1

Answer:

78.9 g Si would need to react with excess nitrogen

Explanation:

The reaction that takes place is:

3Si + 2N₂ → Si₃N₄

Keeping in mind the yield, we can calculate the required moles of Si, using the mass of silicon nitride and its molar mass (140 g/mol):

125 g Si₃N₄ ÷ 140 g/mol = 0.893 mol Si₃N₄

0.893 mol Si₃N₄ * 100/95.0 * $\frac{3molSi}{1molSi_{3}N_{4}}$ = 2.82 mol Si

Finally we convert the moles of Si to g:

2.82 mol Si * 28 g/mol = 78.9 g Si