Presentation on theme: "Stoichiometry, Limiting Reactants and Percent Yield"— Presentation transcript:
1Stoichiometry, Limiting Reactants and Percent Yield
2How many grams of carbon dioxide will be produced when 11 How many grams of carbon dioxide will be produced when 11.6 g of butane (C4H10) burns with oxygen?11.6 g ? g2 C4H O CO H2O2 mole mole11.6 g C4H101 mole C4H10X58.1 g C4H108 mole CO2X2 mole C4H1044.0 g CO2X =1 mole CO235.1 g CO2
3Excess/Limiting Reactants The limiting reactant is the reactant present in the smallest stoichiometric amountIn other words, it’s the reactant you’ll run out of first!The excess reactant will be left over after the reaction.
4Limiting Reactants Example a) 11.6 grams of magnesium react with 54.6 grams of nitric acid. Hydrogen and magnesium nitrate are produced. How many grams of hydrogen are produced?11.6 g g x gMg HNO > H Mg(NO3)2
5Method 1Here are the 2 possible calculations (you really only need to do one of these):1 mol Mg mol HNO g HNO311.6 g Mg X X X = g HNO324.3 g Mg mole Mg mole HNO3We can’t use all the Mg – there’s not enough HNO3 to reactOR1 mole HNO3 1 mole Mg g Mg54.6 g HNO3 X X X = g Mg63.0 g HNO3 mole HNO3 mole MgIf we use all the HNO3 we’ll still have Mg left over
6ALWAYS USE THE LIMITING REACTANT TO FIND THE REQUIRED! Method 1 cont.ALWAYS USE THE LIMITING REACTANT TO FIND THE REQUIRED!1 mole HNO mole H g H254.6 g HNO3 X X X = g H263.0 g HNO3 2 mole HNO mole H2
7Method 2 AND The smaller answer is correct – 0.875g of H2 is formed. HNO3 is the limiting reactant and Mg is the excess reactantWe know this because we used HNO3 to find the correct answer
811.6g Mg – 10.5 g Mg = 1.1 g Mg is left over! Part b…How much magnesium is left over after the reaction?(you may have already done the first step if you happened to do this calculation to find the limiting reactant in method 1)1 mole HNO3 1 mole Mg g Mg54.6 g HNO3 X X X = g Mg63.0 g HNO3 mole HNO3 mole Mg11.6g Mg – 10.5 g Mg = 1.1 g Mg is left over!
9Theoretical YieldThe theoretical yield is the amount of product that can be madeThis is what we calculateThe actual yield is the amount one actually produces and measuresEither measured in the lab or given in the problem
10Percent Yield Actual Yield Theoretical Yield Percent Yield = x 100% A comparison of the amount actually obtained to the amount it was possible to makeActual YieldTheoretical YieldPercent Yield = x 100%