100 grams of magnesium and 2.50 grams of oxygen react together in synthesis reaction to form magnesium oxide. How do you write this balanced reaction?

1 Answer
anor277
Apr 30, 2016

The balanced equation is clearly:

Mg(s) + 1/2O_2(g) rarr MgO(s)

Explanation:

It is abundantly clear that magnesium is in vast molar excess:

i.e. "Moles of metal" = (100*g)/(24.31*g*mol^-1) ~= 5*mol

"Moles of dioxygen" = (2.5*g)/(32.00*g*mol^-1) ~= 0.08*mol

Clearly, O_2 is the limiting reagent, and our calculation proceeds on the basis of the molar quantity of the gas.

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