Step-by-step explanation:
First we need to know that the molar volume of any gas at STP is 22.4 L/mol.
So first let's transform 70 L of nitrogen into moles:
22.4 L --- 1 mol
70 L ---- x mol
x = 3.125 moles of N2
Now let's use the equation ratio to find out the quantity in moles of NaN3:
2 moles of NaN3 ---- 3 moles of N2
y moles of NaN3 ---- 3.125 moles of N2
y = 2.08 moles of NaN3
Let's transform it into grams:
m = n*MM
MM of NaN3 = 65 g/mol
m = 2.08*65
m = 135.4 g
Answer: It is needed 2.08 moles of NaN3 or 135.4 g of it.