Question

Due to its hardness, thermal stability, and resistance to wear, silicon nitride is used in cutting tools. It can be produced through the following chemical reaction. 3 Si(s) + 2 N2(g) „³ Si3N4(s) A combination of 123 g of N2 and 160 g Si is used.

a. What is the theoretical yield of silicon nitride?

b. What mass of the excess reactant remains after the reaction is allowed to progress?

Answer 1

Molar mass of Si = 28 g/mol

Molar mass of N₂ = 2x14 = 28 g/mol'

Molar mass of Si₃N₄ = (3x28) + (4x14) = 140 g/mol

3 Si(s) + 2 N₂(g)   Si₃N₄(s)

According to the balanced equation ,

3 moles of Si reacts with 2 moles of N₂

                        OR

3x28 g of Si reacts with 2x28 g of N₂

160 g of Si reacts with M g of N₂

M = (2x28x160)/(3x28)

   = 106.7 g

So 123-106.7 = 16.3 g of N₂ left unreacted so it is the excess reactant.

Since all the mass of Si completly reacted it is the limiting reactant.

From the reaction ,

3 moles of Si produces 1 mole of Si₃N₄

                           OR

3x28 g of Si produces 140 g of Si₃N₄

160 g of Si produces N g of Si₃N₄

N = ( 160x140) / (3x28)

   = 266.7 g

Therefore the theoretical yield of silicon nitride is 266.7 g