Hello, Molly,
Please look at my answer to a similar question you posted on combustion of propane to get a more detailed explanation of the process used to answer this question.
You have provided a balanced equation, so we can look at the coefficients to create a conversion factor that can be used to provide the answer.
The conversion factor comes from the fact that 2 moles of lithium are required for every 1 mole of calcium:
(2 moles Li)/(1 mole Ca)
We have moles Ca: 0.253 moles Ca. Just multiply that times the conversion factor. Moles Ca cancel, leaving the moles Li required (0.506 moles Li).
Bob
