4Cr (s) + 3O2 (g) →2Cr2O3 (s) calculate how many grams of the product form when 21.4 g of O2 completely reacts

= 67.79 g

Explanation:

The equation for the reaction is;

4Cr (s) + 3O2 (g) →2Cr2O3 (s)

The mass of O2 is 21.4 g, therefore, we find the number of moles of O2;

moles O2 = 21.4 g / 32 g/mol

=0.669 moles

Using mole ratio, we get the moles of Cr2O3;

moles Cr2O3 = 0.669 x 2/3

=0.446 moles

but molar mass of Cr2O3 is 151.99 g/mol

Hence,

The mass Cr2O3 = 0.446 mol x 151.99 g/mol

= 67.79 g