Stoichiometry MolesMass

Remember! You cannot convert directly from a mass of one substance to the mass of another substance! You must always find moles of both substances involved to solve stoichiometry problems

Mole to Mass Problems Given substance in moles converted to moles of unknown substance THEN converted to mass Moles x mole ratio x molar mass

Sample Problem 9-2 In photosynthesis, plants use energy from the sun to produce glucose and oxygen from the reaction of carbon dioxide and water. What mass, in grams, of glucose is produced when 3.00 mole of water react with carbon dioxide? First: write the equation (and balance it!) CO 2 + H 2 O  C 6 H 12 O 6 + O 2 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2

Sample Problem 9-2 Given 3.00 mole H 2 O, find moles of glucose, then mass 3.00 mole H 2 O x 1 mole C 6 H 12 O 6 = mole 6 mole H 2 O glucose mole C 6 H 12 O 6 x g = g 1 moleglucose Answer: 90.1 g C 6 H 12 O 6

Sample Problem 9-3 What mass of carbon dioxide (in grams) is needed to react with 3.00 mole H 2 O in photosynthesis? Stoichiometry can relate products to reactants, reactants to other reactants, or products to other products!

Sample Problem 9-3 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 First find moles, then find mass! 3.00 mole H 2 O x 6 mole CO 2 = 3.00 mole 6 mole H 2 O CO mole CO 2 x g = g 1 moleCO 2 Answer: 132 g CO 2

Now you try it! After reading pages 282 – 283, do Practice Problems 1-3 on page 284.