To calculate the percent yield, we need to compare the actual yield (0.140 kg of copper) with the theoretical yield (the maximum amount of copper that could be produced based on the stoichiometry of the balanced chemical equation).
First, we need to calculate the theoretical yield of copper.
According to the balanced chemical equation, 1 mole of Cu2S reacts to produce 2 moles of Cu.
1 mole of Cu2S has a molar mass of (2 x 63.55 g/mol) + 32.07 g/mol = 159.17 g/mol.
The number of moles of Cu2S can be calculated by dividing its mass by its molar mass:
Number of moles of Cu2S = 0.540 kg / 159.17 g/mol = 3.393 moles
From the stoichiometry of the balanced equation, we know that 1 mole of Cu2S produces 2 moles of Cu. Therefore, the number of moles of Cu produced would be:
Number of moles of Cu = 3.393 moles x 2 = 6.786 moles
The molar mass of Cu is 63.55 g/mol. Multiplying the number of moles of Cu by its molar mass gives us the theoretical yield of Cu:
Theoretical yield of Cu = 6.786 moles x 63.55 g/mol = 431.16 g
Now, we can calculate the percent yield by dividing actual yield by theoretical yield and multiplying by 100:
Percent yield = (0.140 kg / 431.16 g) x 100 = 32.5%
Therefore, the percent yield is approximately 32.5%. Hence, the correct answer choice is A) 32.5%.