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Chemistry 16.3

Chemistry 16.3. Section 12.3-1. Stoichiometry Calculations: Limiting Reagent. Limiting Reagent. 12.3-1.

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Chemistry 16.3

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  1. Chemistry 16.3 Section 12.3-1 Stoichiometry Calculations: Limiting Reagent

  2. Limiting Reagent 12.3-1 • If a carpenter had two tabletops and seven table legs, he could only build one four-legged table. The number of table legs is the limiting factor in the construction of four-legged tables. Similarly, in chemistry, the amount of product made in a chemical reaction may be limited by the amount of one or more of the reactants.

  3. 12.3-1 Limiting Reagent • Limiting Reagents • How is the amount of product in a reaction affected by an insufficient quantity of any of the reactants?

  4. 12.3-1 Limiting Reagent • In a chemical reaction, an insufficient quantity of any of the reactants will limit the amount of product that forms – that is it will cause the reaction to stop because one of the reactants has run out. • The limiting reagent is the reactant runs out first in a chemical reaction. It determines the maximum amount of product that can be made.

  5. 12.3-1 Limiting Reagent • In any chemical reaction, one of the reactants runs out first. This is the limiting reactantas discussed earlier. • The other reactant, the one that was not all used up is called the excess reactant. It is the reactant that is left over. • In general in any chemical reaction, there will be one or more reactants that is/are the limiting reagent and one or more that is/are the excess reagent.

  6. 12.3-1 Limiting Reagent The Chemical Equation for the Preparation of Ammonia

  7. 12.3-1 Limiting Reagent • Steps for Calculating Limiting Reagent: • Choose one product that appears easiest to calculate with. • Determine the # of moles for reactant #1. • Determine the ratio between reactant #1 and the product. • Determine the # of moles of product that can be made from reactant #1. • Determine the # of moles for reactant #2. • Determine the ratio between reactant #2 and the product. • Determine the # of moles of product that can be made from reactant #2. • Compare amounts of product that can be made. The reactant that makes the least amount of product is the limiting reactant.

  8. 12.3-1

  9. 12.3-1

  10. 12.3-1 Evaluate: Do the results make sense? Even though there are more moles of copper (Cu) than there are of sulfur (S), you need two copper atoms to produce one product molecule, whereas you only need one sulfur atom to make the same product. With this in mind and how close the molar quantities are, it makes sense.

  11. 12.3-2 Ammonia, NH3, reacts with oxygen, O2, to form nitrogen monoxide, NO, and water, H2O. If 50.0 g of NH3 react with 100.0 g of O2, which is the excess reactant? Use the following balanced equation: 4 NH3 + 5 O2 → 4 NO + 6 H2O

  12. 12.3-2

  13. 12.3-2 Evaluate: Do the results make sense? Again, even though there are more moles of oxygen (O2) than there are of ammonia (NH3), you need five coppers to produce four product (NO), whereas you only need one sulfur to make the same product. If you had performed this problems using water, H2O as the chosen product, you would still have O2 as the limiting reagent. It was easier to use the NO because of the 1 – 1 ratio between the NH3 and the NO.

  14. The End

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