1. Limiting Reagents

2. We have considered reactions with just the perfect amount of each reactant.

3. Limiting Reagents We have considered reactions with just the perfect amount of each reactant. However, reactions almost never have reactants in perfect amounts.

4. Limiting Reagents We have considered reactions with just the perfect amount of each reactant. However, reactions almost never have reactants in perfect amounts. One reactant is completely used up and another reactant is left over.

5. Limiting and Excess Reactants The limiting reactant is the reactant that is completely used up in a chemical reaction. When the limiting reactant is used up, the reaction stops. No more new product(s) is/are being produced.

6. Limiting and Excess Reactants The limiting reactant is the reactant that is completely used up in a chemical reaction. When the limiting reactant is used up, the reaction stops. No more new product(s) is/are being produced. The excess reactant is the reactant that remains after a reaction is over.

7. Limiting and Excess Reactants The limiting reactant is the reactant that is completely used up in a chemical reaction. When the limiting reactant is used up, the reaction stops. No more new product(s) is/are being produced. The excess reactant is the reactant that remains after a reaction is over. Reactant = Reagent

8. Strategy

9. Determine how much product can be produced by each reactant.

10. Strategy Determine how much product can be produced by each reactant. The reactant that produces the least amount of product is the limiting reactant.

11. Example What is the limiting reactant when 4.80 g of Calcium are mixed with 2.00 g of Nitrogen?

12. Example What is the limiting reactant when 4.80 g of Calcium are mixed with 2.00 g of Nitrogen? Write a balanced equation.

13. Example What is the limiting reactant when 4.80 g of Calcium are mixed with 2.00 g of Nitrogen? Write a balanced equation. 3Ca (s) + N 2 (g)  Ca 3 N 2 (s)

14. Example Convert the masses of the reactants to moles.

15. Example Convert the masses of the reactants to moles. n = m/mm

16. Example Convert the masses of the reactants to moles. n = m/mm n = 4.80 g/40.08g·mol -1 = 0.11976 mol Ca n = 2.00 g/28.02g·mol -1 = 0.07138 mol N 2

17. Example Find the mole ratios and determine which one to use.

18. Example Find the mole ratios and determine which one to use. Ca : N 2 = 3 : 1 Ca : Ca 3 N 2 = 3 : 1 N 2 : Ca 3 N 2 = 1 : 1

19. Example Find the mole ratios and determine which one to use. Ca : N 2 = 3 : 1 Ca : Ca 3 N 2 = 3 : 1 N 2 : Ca 3 N 2 = 1 : 1

20. Example Use the mole ratio to determine the moles of the product from the moles of the reactant.

21. Example Use the mole ratio to determine the moles of the product from the moles of the reactant. Ca : Ca 3 N 2 = 3 : 1 0.040 mol Ca 3 N 2 N 2 : Ca 3 N 2 = 1 : 1 0.071 mol Ca 3 N 2

22. Example The 0.040 mol Ca 3 N 2 produced from Ca is less than the 0.071 mol Ca 3 N 2 produced from N 2.

23. Example The 0.040 mol Ca 3 N 2 produced from Ca is less than the 0.071 mol Ca 3 N 2 produced from N 2. Therefore, the limiting reactant is Ca because the ratio between Ca and Ca 3 N 2 results in the least amount of moles of Ca 3 N 2 produced.

24. Example What is the mass of Calcium Nitride produced?

25. Example What is the mass of Calcium Nitride produced? The reaction stops when all the Ca is used up.

26. Example What is the mass of Calcium Nitride produced? The reaction stops when all the Ca is used up. The moles of Ca 3 N 2 produced from the limiting reactant, Ca, are used to calculate the mass.

27. Example What is the mass of Calcium Nitride produced? The reaction stops when all the Ca is used up. The moles of Ca 3 N 2 produced from the limiting reactant, Ca, are used to calculate the mass. m = n(mm)

28. Example What is the mass of Calcium Nitride produced? The reaction stops when all the Ca is used up. The moles of Ca 3 N 2 produced from the limiting reactant, Ca, are used to calculate the mass. m = n(mm) m = 0.040 mol(148.26 g·mol -1 ) = 5.93 g

29. Example What is the mass of Nitrogen left over after the reaction has stopped?

30. Example What is the mass of Nitrogen left over after the reaction has stopped? Once all the limiting reagent, Ca, has been used up, the reaction stops.

31. Example What is the mass of Nitrogen left over after the reaction has stopped? Once all the limiting reagent, Ca, has been used up, the reaction stops. Once the reaction stops, there is still excess reagent, N 2, left over.

32. Example Use the mole ratio to determine how much of the excess reagent reacted with all of the limiting reagent.

33. Example Use the mole ratio to determine how much of the excess reagent reacted with all of the limiting reagent. Ca : N 2 = 3 : 1

34. Example Use the mole ratio to determine how much of the excess reagent reacted with all of the limiting reagent. Ca : N 2 = 3 : 1 0.040 mol N 2

35. Example Subtract the moles of N 2 used up from the total moles of N 2 available.

36. Example Subtract the moles of N 2 used up from the total moles of N 2 available. 0.071 mol – 0.040 mol = 0.031 mol

37. Example Subtract the moles of N 2 used up from the total moles of N 2 available. 0.071 mol – 0.040 mol = 0.031 mol Determine the mass of N 2 remaining.

38. Example Subtract the moles of N 2 used up from the total moles of N 2 available. 0.071 mol – 0.040 mol = 0.031 mol Determine the mass of N 2 remaining. m = n(mm) m = 0.031 mol(28.02 g·mol -1 ) = 0.88 g

39. Example 3Ca (s) + N 2 (g)  Ca 3 N 2 (s) g mol mole ratio

40. Example 3Ca (s) + N 2 (g)  Ca 3 N 2 (s) g mol mole ratio

41. Example 3Ca (s) + N 2 (g)  Ca 3 N 2 (s) gg mol g