Lead nitrate reacts with sodium sulfide ion to make lead sulfide and sodium nitrate. How much lead sulfide can one make from 15.05g lead nitrate and 10.02 g sodium sulfide?

Pb(NO3)2 = lead nitrate
Na2S = sodium sulfide
PbS = lead sulfide
Na(NO3) = sodium nitrate

Pb(NO3)2 + Na2S = PbS + Na(NO3).

The first thing to do is to balance the equation. Then, figure out how many moles of lead nitrate you're starting with and how many moles sodium sulfide you're starting with. You then determine if one or the other is in excess.

For example, H2 + 1/2 O2 = H2O

If I have 2 moles of H2 and 50 moles of O2, O2 is obviously in excess (since I only need 1 mole) so only 1 mole of it will react.

Once you've figured that out, you can use the balanced equation to tell how many moles of lead sulfide you can make (assume the reaction goes to completion). Then, determine the molecular weight of lead sulfide and use that to calculate the weight of lead sulfide that you produce.