Hello, Jade,
We can convert the number of moles of any element or compound, into the number of atoms or molecules using avogadro's number, 6.02x1023.
1 mole of anything is 6.02x1023 of whatever item is being described. The word mole, in this problem, represents a unit of count of the number of SO3 molecules. One mole of SO3 would have 6.02x1023 of those molecules.
We can express this as a conversion factor:
(6.02x1023 molecules SO3)/(mole SO3)
Now use this factor to convert 1.14 moles SO3 to molecules SO3.
(1.14 moles SO3 )*((6.02x1023 molecules SO3)/(mole SO3)) = 6.86x1023 molecules SO3
Bob