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Limiting Reactants & Percent Yield Section 12.3. If we have…how many sets can we make? Limiting reactant = the reactant that runs out first causing the.

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Presentation on theme: "Limiting Reactants & Percent Yield Section 12.3. If we have…how many sets can we make? Limiting reactant = the reactant that runs out first causing the."— Presentation transcript:

1 Limiting Reactants & Percent Yield Section 12.3

2 If we have…how many sets can we make? Limiting reactant = the reactant that runs out first causing the reaction to stop Excess reactant = reactant that does not get completely used up during a reaction With this left over Excess

3 Steps to solve limiting reactants problems 1.Split into 2 problems 2.Solve each problem 3.Pick smallest answer -Smallest answer comes from limiting reactant -Largest answer comes from excess reactant

4 Calculating product when reactant is limiting   If we had 12 moles of nitrogen and 18 moles of hydrogen, what is the maximum number of moles of NH 3 that could be produced? N 2 + 3H 2  2 NH 3

5 Calculating product when reactant is limiting   If we had 112 grams of nitrogen and 18 grams of hydrogen, what is the maximum number of grams of NH 3 that could be produced? N 2 + 3H 2  2 NH 3 2(14) 2(1) (14) 2(1) Remember… NitrogenHydrogen Pick lowest number Therefore Hydrogen is your limiting reactant

6 Calculating product when reactant is limiting   With 48 grams of magnesium and 48 grams of oxygen available, how much product can be formed? 2Mg + O 2  2 MgO (16) (16) Magnesium Oxygen Pick lowest number Therefore Magnesium is your limiting reactant and oxygen is the excess reactant

7 Limiting Reactants Practice III   How many grams of sodium chloride can be produced in the following reaction with 150 grams of sodium and 200 grams of chlorine? 2Na + Cl 2  2 NaCl 23 2(35.5) (35.5) SodiumChlorine Pick lowest number

8 Limiting Reactants Practice III   In the above reaction, how many more grams of chlorine will be required to fully react with the remaining sodium?   We need to figure out how many grams of chlorine is needed to react with 150 grams of sodium 2Na + Cl 2  2 NaCl 23 2(35.5) (35.5) 71 Sodium Chlorine needed = 231 g Chlorine given (from problem) = 200 g Additional Chlorine needed = 31 g

9 Percent Yield  Actual yield = the actual amount of product formed during an experiment  Theoretical yield = amount of product that could be produced according to calculations  Percent yield = ratio of actual and theoretical yield

10 Percent Yield Practice I 1.A student uses stoichiometry to calculate the predicted yield of CO 2 in a chemical reaction as 323 g. When the student mixes the chemicals to make the CO 2, he finds that the reaction only produces 308 g of CO 2. What is the percent yield?

11 2.In the reaction, how many grams of potassium oxide can be produced with 78 grams of potassium and 140 grams of boron oxide? 6 K + B 2 O 3  3 K 2 O + 2 B (10.8)+3(16) 2(39.1) PotassiumBoron Oxide Pick lower number

12  Problem 2 continued  If the actual yield from the above reaction was 81 grams, what is the percent yield?  Actual yield = 81 grams  Theoretical yield = g (from last slide)

13 3. The actual yield in the above reaction was 39 grams of ammonium. Using 84 grams of nitrogen and 8 grams of hydrogen, what is the percent yield? -first we must calculate the theoretical yield of product which means we need to find our limiting reactant N 2 + 3H 2  2 NH 3 2(14) 2(1) NitrogenHydrogen Pick lower number

14  Problem 3 continued  Actual yield = 39 grams  Theoretical yield = 45.3 g (from last slide)


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