2ReviewIn a chemical reaction, how do we relate moles of one compound to moles of another?What are the four steps to go from mass of one reactant or product to the mass of another?MOLE RATIO!2A + BA2B1. Write the balanced equation2. Convert mass of given to moles3. Use the mole ratio from the balanced equation to find moles of the unknown4. Convert moles of the unknown to mass of the unknown
3Chemical Construction In your group, you have a beaker of hydrogen (H2) and a beaker of carbonYou need to make as many methane molecules (CH4) as you can!
4Activity AnalysisWhich element limited the number of methane molecules you could make?Which element was present in excess amounts?Did the element present in excess affect the number of methane molecules you could make?Why doesn’t the carbon limit the number of methane molecules you could make, even though they are present in the smallest quantity?
5Limiting ReactantReactants are rarely present in amounts that correspond exactly to the mole ratios in the balanced equationLimiting reactant: a reactant that is completely consumed during a chemical reaction and limits the amount of product that can be formedExcess reactant: a reactant that remains after a reaction is over
6Limiting Reactant 2 mol 1 mol 2 mol L.R. 2 mol 2 mol 4 mol 1 mol L.R. The limiting reactant forms the smallest amount of productUse stoichiometry to determine which reactant produces the smallest amount of product
7Practice ProblemLithium nitride reacts with water to form ammonia and lithium hydroxide, according to the following balanced chemical equation:If 4.87 g of lithium nitride reacts with 5.80 g of water, find the limiting reactant.
8YieldTheoretical yield is the maximum amount of product that can form in a chemical reactionCalculated by assuming that all of the limiting reagent has reacted to form the productIn reality:Many reactions do not go to completionOther reactions, called side reactions, may occurSome product may be lost during purificationWhat are some things that might prevent us from reaching the theoretical yield?
9YieldThe actual yield is the amount of a product that is actually obtained from a chemical reactionThe actual yield is almost always less than the theoretical yieldActual Yield is an experimentally determined quantityPercent yield:% Yield = actual yield x 100theoretical yield
10Crucial Information for Chemists Consider the synthesis of Diazonamide AChemical synthesis in pharmaceutical industry or industrial chemistry involves many stepsLow percent yield in each step results in a tiny over all yieldWasted reactants translates into loss of money and resources82%95%86%65%88%67%88%85%80%60%50%R. R. Knowles, J. Carpenter, S. B. Blakey, A. Kayano, I. K. Mangion, C. J. Sinz, D. W. C. MacMillan, Chem. Sci., 2011, 2,
11Practice ProblemAmmonia can be prepared by reacting nitrogen gas with hydrogen gas:When 7.5 x 101 g of nitrogen reacts with sufficient hydrogen, the theoretical yield of ammonia is 9.10g. If 1.72 g of ammonia is obtained by experiment, what is the percentage yield of this reaction?