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Limiting reactants
 

Limiting reactants

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    Limiting reactants Limiting reactants Presentation Transcript

    • Limiting reactants →
    • Problem solving Aim: Be able to calculate: A. Which reactant (if any) is limiting? B. What mass or volume of product can be formed?
    • A. Which reactant is limiting? 750g of ammonia and 750 g of oxygen are combined. 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(l) 1 Calculate moles of each reactant: moles = mass/mr Moles NH3 = 750 / 17.03 = 44 moles Moles O2 = 750 / 32 = 23.4 2 Check the required ratio compared to the actual ratio. Require 5mole O2 / 4mole NH3 = 1.25moles O2 / 1mole NH3 Available 23.4mole O2 /44mole NH3 = 0.523moles O2 / 1 mole NH3 Oxygen is the limiting reagent!
    • B. What mass of NO can we form? 750g of ammonia and oxygen are combined. 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(l) 1. Work out moles of limiting reactant Previous slide moles O2 = 23.4 2 Use the product / reactant mole ratio to work out moles of product 23.4 x (4/5) = 18.72 moles of NO 3 Convert moles to mass Mass = moles x mr = 18.72 x 30.1 = 562g of NO
    • 125g of Cl2 and 125g of C were added to an excess of TiO2 and the following reaction occurred: TiO2(s) + 2Cl2(g) + C(s) → TiCl4(l) + CO2(g) A. Which reactant is limiting? 1 Calculate moles of each reactant: moles = mass/mr Moles Cl2 = 125 / 71 = 1.76 moles Moles C = 125 / 12 = 10.4 moles 2 Check the required ratio compared to the actual ratio. Require 2moles Cl2 / 1mole C Available 1.76moles Cl2 /10.4 moles C = 0.17 Cl2 / 1 mole C Cl2 is the limiting reagent
    • 125g of Cl2 and 125g of C were added to an excess of TiO2 and the following reaction occurred: TiO2(s) + 2Cl2(g) + C(s) → TiCl4(l) + CO2(g) B What mass of TiCl4 can be produced? 1. Work out moles of limiting reactant Previous slide Cl2 = 1.76 moles 2 Use the product / reactant mole ratio to work out moles of product 1.76 x (1/2) = 0.88 moles of TiCl4 3 Convert moles to mass Mass = moles x mr = 0.88 x 189.7 = 167g of TiCl4
    • Practice 1. 356g of CO and 65g of H2 react according to the equation: CO(g) + H2(g) → CH3OH(l) Which reactant is limiting and what is the maximum mass of methanol that can be formed? 2. The thermite reaction is used to produce molten Iron: Fe2O3(s) + 2Al(s) → 2Fe(l) + Al2O3(s) 50g of Al and 50g Fe2O3 is used. Which reactant is limiting? What is the maximum mass of iron that can be produced? 3. A 2l bottle contains 800cm3 of propane and the remainder is oxygen. C3H8 + 5O2 → 3CO2 + 4H2O Which reactant is limiting? What is the maximum volume of CO2 that can be produced? Why might a greater volume of CO2 actually be produced?!?
    • Answers 1. CO is limiting and 407g of CH3OH can be produced 2. Fe2O3 is limiting and 35g of Fe can be produced 3. O2 is limiting and 0.72dm3 (= 720cm3 ) of CO2 could be formed. Exothermic reaction causes expansion of gases.
    • Extension Design your own question on limiting reactants. Develop a different method for solving these types of problems that will work in every case.
    • Extension Design your own question on limiting reactants. Develop a different method for solving these types of problems that will work in every case.