In the reaction cap c plus cap o sub 2 rightarrow CO sub 2 , 18 g of carbon react with oxygen to produce 72 g of carbon dioxide. What mass of oxygen would be needed in the reaction?

By conservation of mass, the mass of the reactants equals the mass of the products. The 72 g of carbon dioxide consists of 18 g of carbon plus the oxygen that reacted, so the oxygen mass is 72 − 18 = 54 g. The correct choice is 54 g.

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