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Limiting Reactants & Percent Yield

Limiting Reactants & Percent Yield. Section 12.3. With this left over. Excess. 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.

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Limiting Reactants & Percent Yield

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  1. Limiting Reactants & Percent Yield Section 12.3

  2. With this left over Excess 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

  3. Steps to solve limiting reactants problems • Split into 2 problems • Solve each problem • 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 NH3 that could be produced? N2 + 3H2 2 NH3

  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 NH3 that could be produced? N2 + 3H2 2 NH3 2(14) 2(1) 14 + 3 28 2 17 Remember… Nitrogen Hydrogen 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 + O2 2 MgO 24.3 2(16) 24.3 + 16 32 40.3 Oxygen Magnesium 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 + Cl2 2 NaCl 23 2(35.5) 23 + 35.5 71 58.5 Sodium Chlorine 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 + Cl2 2 NaCl 23 2(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 • A student uses stoichiometry to calculate the predicted yield of CO2 in a chemical reaction as 323 g. When the student mixes the chemicals to make the CO2, he finds that the reaction only produces 308 g of CO2. What is the percent yield?

  11. 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 + B2O3 3 K2O + 2 B 39.1 2(10.8)+3(16) 2(39.1)+16 69.6 94.2 Potassium Boron 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 = 93.95 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 N2 + 3H2 2 NH3 2(14) 2(1) 14+ 3 28 2 17 Nitrogen Hydrogen Pick lower number

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

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