Since the reaction is
[tex]Na_2O+H_2O\to2NaOH[/tex]We would first need to balance it, but we can see that it was already balanced.
So, we can just apply the stoichiometry.
Assuming all the Na₂O react, we can just compair the coefficients of Na₂O and NaOH to calculate how much we need.
From the equation, we see that each 1 mol of Na₂O produce 2 moles of NaOH, so using rule of three we have:
Na₂O --- NaOH
x --- 1.57 mol
1 mol --- 2 mol
So we have the relation:
[tex]\begin{gathered} \frac{x}{1mol}=\frac{1.57}{2} \\ x=0.785mol \end{gathered}[/tex]So, we need 0.785 mol of Na₂O.
