Question

What is the molar ratio for the chemical reaction $ Al + {O_2} \to A{l_2}{O_3} $ ?

Answer 1

Hint: The molar ratio means how many moles of product were formed from certain moles or certain amounts of reactant. From the balanced chemical equation, the ratio of the moles reacted gives the mole ratio of the chemical reaction.

Complete Step By Step Answer:
The number of moles means the ratio of the mass of the solute to the molar mass of the compound. Whereas the molar ratio gives the information about how many moles of each reactant were reacted to form a product.
Thus, the moles of each reactant in a balanced chemical equation gives the mole ratio.
Given reaction is $ Al + {O_2} \to A{l_2}{O_3} $
In the above reaction, aluminium and oxygen gas were reacted with each other leads to the formation of aluminium oxide with molecular formula of $ A{l_2}{O_3} $
In the above given reaction, the number of oxygen, and aluminium atoms were not balanced. The balanced chemical equation will be:
 $ 4Al + 3{O_2} \to 2A{l_2}{O_3} $
From the above balanced chemical equation, it was clear that $ 4 $ moles of aluminium was reacted with $ 3 $ moles of oxygen gas to form $ 2 $ moles of aluminium oxide.
The molar ratio of a chemical reaction will be the ratio of moles of aluminium and moles of oxygen which can be written as $ 4:3 $
Thus, the molar ratio for the chemical reaction $ Al + {O_2} \to A{l_2}{O_3} $ is $ 4:3 $ .

Note:
From the mole ratio of reactants only the molar ratio of a chemical reaction will be determined. While calculating the moles of reactants, only reactant moles must be considered, in case of reactants like oxygen $ \left( {{O_2}} \right) $ the atoms should not be considered. As in oxygen $ \left( {{O_2}} \right) $ the moles and atoms will be of different values.