To determine why 1.5 moles is equivalent to 39 grams of LiF, we need to consider the molar mass of LiF. The molar mass of a compound represents the total mass of one mole of that substance.

The molar mass of LiF can be calculated by adding the atomic masses of lithium (Li) and fluorine (F).

Atomic mass of Li = 6.941 g/mol

Atomic mass of F = 18.998 g/mol

Molar mass of LiF = (6.941 g/mol) + (18.998 g/mol) = 25.939 g/mol

Now, we can use the molar mass to determine the mass of 1.5 moles of LiF:

Mass = number of moles × molar mass

Mass = 1.5 mol × 25.939 g/mol = 38.9085 g

Therefore, 1.5 moles of LiF is equivalent to approximately 38.91 grams, which is close to the given value of 39 grams.