Determining the Limiting Reactant in a Chemical Reaction

Which is the limiting reactant when silicon dioxide and carbon are heated?

Given 70.0 g of SiO2 and 50.0 g of C, which is the limiting reactant?

Answer:

The limiting reactant in the reaction of silicon dioxide and carbon is SiO₂.

When silicon dioxide (sand) and carbon are heated, the products are silicon carbide, SiC, and carbon monoxide, CO. Silicon carbide is a ceramic material that tolerates extreme temperatures and is used as an abrasive and in the brake discs of cars.

The limiting reactant is the substance that is completely used up in a chemical reaction and determines the amount of product that can be formed. In this case, to determine the limiting reactant, we need to compare the amount of each reactant to the balanced chemical equation:

SiO₂ + 3C → SiC + 2CO

First, we need to calculate the moles of each reactant:

70.0 g SiO₂ × (1 mol SiO₂ / 60.1 g SiO₂) = 1.16 mol SiO₂

50.0 g C × (1 mol C / 12.0 g C) = 4.17 mol C

Next, we need to compare the mole ratio of each reactant to the balanced equation:

1.16 mol SiO₂ / 1 mol SiO₂ = 1.16

4.17 mol C / 3 mol C = 1.39

Since the ratio for SiO₂ is smaller (1.16), it is the limiting reactant. Therefore, the reaction will use up all of the SiO2 and produce 1.16 mol of SiC and 2.32 mol of CO. The excess carbon will not be used in the reaction.