Copper(l) sulfide can react with oxygen to produce copper metal by the reaction cu2s + o2 => 2cu + so2. if 5.00 g of cu2s is used, then what is the theoretical yield of cu?

To answer this problem, we write first the stoichiometric equation. Thus we have,

Cu2S + O2 => 2Cu + SO2

Next, we check if the equation is balanced or not.

(left)     (right)
2 Cu  = 2 Cu
1 S  =  1 S
2 O = 2 O

So the stoichiometric equation is balanced, let's proceed in solving the theoretical yield of Cu given 5 g of Cu2S.

First, we solve for Cu2S in moles,
5 g Cu2S x 1 mol Cu2S   = 0.0314 mol Cu2S
                159.16 g Cu2s

Secondly, convert moles of Cu2S to moles Cu. Note for every mole of Cu2S we get 2 moles of Cu. Thus,

0.0314 mo Cu2S x    2 mol Cu      = 0.0628 mole Cu
                                1 mol Cu2S

Lastly, we convert mole Cu to g Cu via multiplying by Cu's MW.

0.0628 mole Cu x 63.546 g Cu   = 3.99 g Cu or 4 g Cu
                                1 mole Cu

ANSWER: 4 g Cu