Given: $10$ g Cu reacts with $10$ g $O_2$.
Skeletal equation: $" "Cu + O_2 -> CuO_2$
balanced equation is the same as the skeletal equation.
molar masses:
$63.546 g/(mol) " "Cu; " " 2(15.999) = 31.998 g/(mol) " "O_2$
$63.546 + 31.998 = 95.544 g/(mol) " "CuO_2$
Find the :
$10 g Cu xx (1 mol Cu)/(63.546 g Cu) xx (1 mol CuO_2)/(1 mol Cu) = .1574 mol " " CuO_2$
$10 g O_2 xx (1 mol O_2)/(31.998g O_2) xx (1 mol CuO_2)/(1 mol Cu) = .1325 mol " " CuO_2$
Cu is the limiting reagent.
$O_2$ is in excess.
Find the amount of $O_2$ used:
$.1574 mol " " CuO_2 xx (1 mol O_2)/(1 mol CuO_2) xx (31.998 g O_2)/(1 mol O_2) ~~ 5 g " "O_2 $
Find the mass of $O_2$ in excess:
$10 g - 5 g ("used")= 5 g$ in excess
Find the mass of produced product $CuO_2$:
$.1574 mol " " CuO_2 xx (95.544 g CuO_2)/(1 mol CuO_2) = 15.04 g " "CuO_2$