Equal masses of and are heated together to form . What fraction of the original mass of excess reactant is left unreacted?

Question

Equal masses of  and  are heated together to form . What fraction of the original mass of excess reactant is left unreacted?

Canvas Classes · Accepted Answer

Strategy:
 Determine the excess reactant by comparing the equal masses of Iron and Sulfur to their reacting mass ratio (  to  ). The fraction left over is the unreacted mass of the excess species divided by its original mass.

Step 1: Identify limiting and excess reactants
Reacting ratio is . 
If we start with  of each:
-   needs  .
-  of  remains unreacted ().
Thus,  is in excess.

Step 2: Calculate the unreacted fraction

Rounding gives .

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