EXAM #2: Chapter 5.1 Stoichiometry

5.1 Example #2: How many molecules of NH3 can you make if you have 228 atoms of H2?

76 molecules NH3 From the formula, we know that one molecule of NH3 has three H atoms. Use that fact as a conversion factor: ---(picture)

5.1 Example #1: How many molecules of SO3 are needed to react with 144 molecules of Fe2O3 given this balanced chemical equation? F e 2 O 3 ( s ) + 3 S O 3 ( g ) ⟶ F e 2 ( S O 4 ) 3

432 molecules of SO3 We use the balanced chemical equation to construct a conversion factor between Fe2O3 and SO3. The number of molecules of Fe2O3 goes on the bottom of our conversion factor so it cancels with our given amount, and the molecules of SO3 go on the top. Thus, the appropriate conversion factor is 3 molecules SO3 ------------------ 1 molecule Fe2O3 Starting with our given amount and applying the conversion factor, the result is ----(picture) We need 432 molecules of SO3 to react with 144 molecules of Fe2O3.