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stoicheion - elementmetron- measure

Jeremias Benjaim Richter(1762-1807)

What you need to know...Molar ratios, molar masses, as well as interpreting and balancing equations.




To solve stoichiometry problems...Balance the equation, convert mass to moles, construct the proportion, convert moles to mass

The source for molar ratios comes from the coefficients in the balanced equation!

N2 + 3H2 ---> 2NH3What is the molar ratio between N2 and H2?1:3 because there is 1 N2 molecule and 3 H2 molecules.What is the molar ratio between NH3 and H2?2:3 because there are 2 NH3 molecules and 3 H2 molecules.

2SO2 + O2 ---> 2SO3What is the molar ratio between O2 and SO3?1:2 because there is 1 O2 molecule and 2 SO3 molecules.What is the molar ratio between SO2 and O2?2:1 because there are 2 SO2 molecules and 1 O2 molecule.

PCl3 + Cl2 ---> PCl5What is the molar ratio between PCl3 and Cl2?1:1 because there is 1 PCl3 molecule and 1 Cl2 molecule.What is the molar ratio between PCl5 and PCl3?1:1 because there is 1 PCl5 molecule and 1 PCl3 molecule.




To solve mole-mole problems...Balance the equation, cross multiply, then divide.

N2 + 3H2 ---> 2NH3We want to produce 2.75 mol of NH3. How many moles of nitrogen would be required?NH3/N22/12.75/x2.75/x = 2/12.75*1 = 2.75x*2 = 2x2.75 = 2x2.75/2 = 1.382x/2 = x1.38 = x1.38 mol of nitrogen is required.

N2 + 3H2 ---> 2NH3Suppose 6.00 mol of H2 reacted with sufficient nitrogen. How many moles of ammonia would be produced?NH3/H22/3x/6x/6 = 2/3x*3 = 3x6*2 = 123x/3 = x12/3 = 4x = 44 moles of ammonia will be produced.

N2 + 3H2 ---> 2NH3If we have 2.00 mol of N2 reacting with sufficient H2, how many moles of NH3 will be produced?NH3/N22/1 (2 NH3 molecules & 1 N2 molecule)x/2 (x is the number we are looking for)Set up problem: x/2 = 2/1x*1 = x2*2 = 4x = 44 mol of NH3 will be produced.

Make sure that the numbers and molecules are in the same relative position!!!


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