How many grams and how many moles two different questions?

Question

For the reaction
NH3 + O2 → NO + H2O
how many moles of H2O are produced from the complete reaction of 2.18 moles of NH3 ?

For the reaction
SO2 + O2 --> SO3
how many grams of SO2 are needed to completely react with 64.00 g of O2 ?

Answer 1

First step is to balance:
4NH3 + 5O2 → 4NO + 6H2O

For each molecule of NH3 you produce 1.5 molecule of H2O

For 2.18 moles of NH3 you produce (1.5*2.18=) 3.27 moles of H2O

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SO2 + O2 → SO3
Balance:
2SO2 + O2 → 2SO3

64 g of O2 is 2 moles (64/32)

Multiply everything by 2:

4SO2 + 2O2 → 4SO3

1 mole of SO2 = (32.07 + 32 = ) 64.07 g
4 moles of SO2 = 256.28 g