How many moles of n2 are needed to react with 0.500 mol of lithium

Answer 1

Write the equation and balance it.
6Li + N2 ==> 2Li3N

Then it's a matter of the proper stoichiometry. Here is a sample problem I posted on stoichiometry. Just follow the steps.
http://www.jiskha.com/science/chemistry/stoichiometry.html

Answer 2

You have to have a reaction.

6Li + N2>>2Li3N

You need 1/6 * .5moles of N2

Answer 3

0.500/6