1.0 g of magnesium is burnt with 0.56 g O2 in a closed vessel. Which reactant is left in excess and how much (At. wt. Mg = 24; O = 16)

1 g of Magnesium is Burnt with 0.56 g O2 in a Closed Vessel

A
Mg,0.44 g
B
O₂, 0.28 g
C
Mg, 0.16 g
D
O₂, 0.16 g

Solution:

The balanced chemical reaction is shown below:
   $Mg + \frac{1}{2} O_{2} \to MgO$
Moles:    $\frac{1.0}{24}; \frac{0.56}{32}$

   $\frac{0.5}{12}; \frac{0.07}{4}$

$\frac{0.5}{12} - x; \frac{0.07}{4} - \frac{x}{2}$
Oxygen is limiting reagent so, $\frac{0.07}{4} - \frac{x}{2} = 0$
$x = \frac{0.07}{2}$
Excess Mg = $\frac{0.5}{12} - \frac{0.07}{2} mol$
Mass of Mg is = 1 − 0.07 × 12 = 0.16 g
Thus, when 1.0 g of magnesium is burnt with 0.56 g O₂ in a closed vessel, 0.16 g of Magnesium is left in excess.