University:
Campbell University
Course:
CHEM 111 | General Chemistry I
Academic year:

2024
Views:

395

Pages:

2
Author:

cinquennehgz

Limiting Reagent Handout - Notes – Limiting Reagent - Chemical reactions are like cooking. You need to mix the correct amount of “ingredients” or your cake won’t rise. - If you add too much of one or more ingredients then the cake tastes poor. In chemistry if you add too much of one of more reactants (ingredients) the product (cake) ends up being wasted. Instructions – go to the address below on a laptop. Figure out which ingredient decides how many sandwiches can be made each time. Test your ideas by completing the game. Ex. – building a bike. A bike has 1 frame, 2 tires, 1 handle bar, 1 seat and 2 pedals. If you have 2 frames, 3 handlebars, 1 seat and 9 petals, 4 tires how many bikes can you build? Answer – 1 bike! With 2 tires, 1 frame, 2 handlebars and 7 pedals. - Chemical reactions work the same way. The chemical with the least amount needed for the reaction to work will limit how much product is made. Ex. 1 - 2 H2 (g) + O2 Parts = (g) 2 H2O (l) 2 H2 and 1 O2 This will only make 2 water! - If we have 20.0 of H2 (g) reacted with 100.0 O2 (g), which reactant is in excess? Remember, the coefficients used to balance the reaction above are the mole equivalencies for each molecule. That is, I need twice as many moles of hydrogen gas as the number of moles of oxygen gas. Answer – change grams to moles and use the mole ratio to see if there is enough oxygen to react all of the oxygen. 20.0 × . × × . = 158.735 This means I need 159 g of O2 I only have 100.0 of O2 so oxygen is limiting!!!! 1 Ex. 2 – If 56.8 of FeCl2, 14.0 of KNO3 and 40.0 of HCl are reacted according to the equation below, which chemical is the limiting reagent? ___ FeCl2 + ___ KNO3 + ___ HCl Balance First!!!! ___ FeCl3 + ___ NO + ___ H2O + ___ KCl 3 FeCl2 + KNO3 + 4 HCl 3 FeCl3 + NO + 2 H2O + KCl Pick one of the products that you will convert each reactant to. (choose NO as its only 1 mole) 56.8 × 14.0 (' × 40.0 × !" #.$% !" )&* . )&* " #.+# " × × & & × )&* & + !" " × . & × & × . & & . & & smallest so limiting is KNO3 = 4.48 ' = 4.15 '  = 8.22 ' as KNO3 is chemical that made the smallest NO amount Ex. 3 - How much excess of each of the other reactants was there? )&* !" #.$% !" !" 14.0 (' × . So . . . 56.8 − 52.651 = 4.149 → 14.0 (' × . So . . . 40.0 − 20.19 = 19.806 → )&* )&* )&* × × )&* + " )&* × × #.+# " " = 52.651 4.1 /0 1233 = 20.1935 19.8 /0 1233 2