Theoretical Value Question: Chemistry

Question

Unbalanced Equation:

Cu + SO₂ → Cu₂O + Cu₂S

Calculate the theoretical yield (in grams) of Cu₂S in the reaction between 0.138 g Cu and 0.626 g SO₂.

Answer 1

Hello Daisy

 

Let's first balance the chemical reaction.

 

6Cu + SO₂ → 2Cu₂O + Cu₂S

 

We need to first determine whether Cu or SO₂ is the limiting reagent in this reaction using stoichiometry.  The theoretical yield of Cu₂S is based on the # of moles of the limiting reagent.  Molar mass of Cu is 64 g/mol, SO₂ is 64 g/mol and Cu₂S is 159 g/mol.  Mole ratio of Cu to Cu₂S is 6:1 and SO₂ to Cu₂S is 1:1.

 

Convert the mass of Cu and SO₂ to moles of Cu₂S.  The reactant that produces the lower amount of Cu₂S is the limiting reagent.

 

0.138 g Cu x (1 mol Cu / 64 g Cu) x (1 mol Cu₂S / 6 mol Cu) = 0.000359 mol Cu₂S

 

0.626 g SO₂ x (1 mol SO₂ / 64 g SO₂) x (1 mol Cu₂S / 1 mol SO₂) = 0.00978 mol Cu₂S

 

From above, you can see that Cu forms less Cu2S, therefore, it is the limiting reagent.

 

Theoretical Yield = 0.000359 mol Cu₂S x (159 g Cu₂S / 1 mol Cu₂S) = 0.0571 g Cu₂S