limiting reagents. we have considered reactions with just the perfect amount of each reactant
TRANSCRIPT
Limiting Reagents
Limiting Reagents
• We have considered reactions with just the perfect amount of each reactant.
Limiting Reagents
• We have considered reactions with just the perfect amount of each reactant.
• However, reactions almost never have reactants in perfect amounts.
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.
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.
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.
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
Strategy
Strategy
• Determine how much product can be produced by each reactant.
Strategy
• Determine how much product can be produced by each reactant.
• The reactant that produces the least amount of product is the limiting reactant.
Example
• What is the limiting reactant when 4.80 g of Calcium are mixed with 2.00 g of Nitrogen?
Example
• What is the limiting reactant when 4.80 g of Calcium are mixed with 2.00 g of Nitrogen?
• Write a balanced equation.
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) + N2 (g) Ca3N2 (s)
Example
• Convert the masses of the reactants to moles.
Example
• Convert the masses of the reactants to moles.n = m/mm
Example
• Convert the masses of the reactants to moles.n = m/mmn = 4.80 g/40.08g·mol-1 = 0.11976 mol Can = 2.00 g/28.02g·mol-1 = 0.07138 mol N2
Example
• Find the mole ratios and determine which one to use.
Example
• Find the mole ratios and determine which one to use.Ca : N2 = 3 : 1Ca : Ca3N2 = 3 : 1N2 : Ca3N2 = 1 : 1
Example
• Find the mole ratios and determine which one to use.Ca : N2 = 3 : 1Ca : Ca3N2 = 3 : 1N2 : Ca3N2 = 1 : 1
Example
• Use the mole ratio to determine the moles of the product from the moles of the reactant.
Example
• Use the mole ratio to determine the moles of the product from the moles of the reactant.Ca : Ca3N2 = 3 : 10.040 mol Ca3N2
N2 : Ca3N2 = 1 : 10.071 mol Ca3N2
Example
• The 0.040 mol Ca3N2 produced from Ca is less than the 0.071 mol Ca3N2 produced from N2.
Example
• The 0.040 mol Ca3N2 produced from Ca is less than the 0.071 mol Ca3N2 produced from N2.
• Therefore, the limiting reactant is Ca because the ratio between Ca and Ca3N2
results in the least amount of moles of Ca3N2 produced.
Example
• What is the mass of Calcium Nitride produced?
Example
• What is the mass of Calcium Nitride produced?
• The reaction stops when all the Ca is used up.
Example
• What is the mass of Calcium Nitride produced?
• The reaction stops when all the Ca is used up.
• The moles of Ca3N2 produced from the limiting reactant, Ca, are used to calculate the mass.
Example
• What is the mass of Calcium Nitride produced?
• The reaction stops when all the Ca is used up.
• The moles of Ca3N2 produced from the limiting reactant, Ca, are used to calculate the mass.m = n(mm)
Example
• What is the mass of Calcium Nitride produced?
• The reaction stops when all the Ca is used up.
• The moles of Ca3N2 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
Example
• What is the mass of Nitrogen left over after the reaction has stopped?
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.
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, N2, left over.
Example
• Use the mole ratio to determine how much of the excess reagent reacted with all of the limiting reagent.
Example
• Use the mole ratio to determine how much of the excess reagent reacted with all of the limiting reagent.
• Ca : N2 = 3 : 1
Example
• Use the mole ratio to determine how much of the excess reagent reacted with all of the limiting reagent.
• Ca : N2 = 3 : 1
• 0.040 mol N2
Example
• Subtract the moles of N2 used up from the total moles of N2 available.
Example
• Subtract the moles of N2 used up from the total moles of N2 available.
• 0.071 mol – 0.040 mol = 0.031 mol
Example
• Subtract the moles of N2 used up from the total moles of N2 available.
• 0.071 mol – 0.040 mol = 0.031 mol• Determine the mass of N2 remaining.
Example
• Subtract the moles of N2 used up from the total moles of N2 available.
• 0.071 mol – 0.040 mol = 0.031 mol• Determine the mass of N2 remaining.
• m = n(mm)m = 0.031 mol(28.02 g·mol-1) = 0.88 g
Example
3Ca (s) + N2 (g) Ca3N2 (s)g
molmolmole ratio
Example
3Ca (s) + N2 (g) Ca3N2 (s)g
molmolmole ratio
Example
3Ca (s) + N2 (g) Ca3N2 (s)g g
mol
molmol
g