University:
University of North Carolina at Charlotte
Course:
CHEM 1251 | General Chemistry I
Academic year:

2024
Views:

94

Pages:

5
Author:

Kamila P.

CHAPTER 8 CHEMICAL REACTIONS Pizza Stoichiometry Back to the pizza recipe: 1 crust + 5oz tomato sauce + 2oz cheese → 1 pizza 1 crust 10 cups of cheese 15 ounces of tomato sauce 3 pizzas! LIMITING REACTING, THEORETICAL YIELDS, AND ACTUAL YIELDS • In the pizza analogy, the tomato sauce is the limiting reactant, the reactant that makes the least amount of product. • The maximum number of pizzas that can be made depends on the tomato sauce. • In chemical reactions, this is called the theoretical yield. • Theoretical yield = amount of product that can be made in a chemical reaction based on the amount of limiting reactant. 15 ounces of tomato sauce → 3 pizzas! • Imagine that while making these 3 pizzas, you drop one of them on the floor. • The actual yield is now 2 pizzas! (Actual yield = amount of product made) BACK TO CHEMISTRY ... • Nitrogen and hydrogen gas react to form ammonia gas according to this reaction: N2(g) + 3H2(g) → 2NH3(g) • If a flask contains a mixture of reactants represented by the picture on the left, which picture on the right (a,b,c,d) represents the mixture in the flask after the reactions have reacted as much as possible? ACTUAL YIELD, EFFICIENCY OF OUR REACTION • Actual yield is about efficiency of the reaction. • To determine your efficiency in making pizzas, you can calculate a PERCENT YIELD (what percent of the theoretical amount of pizza did you actually make) % yield = actual yield theoretical yield × 100% • What was your percent yield in this pizza example? actual yield = 2 pizzas (end of reaction) theoretical yield = 3 pizzas % yield = (2 pizzas / 3 pizzas) × 100% = 66.7% THEORETICAL YIELD Ammonia, NH₃, can be synthesized by the reaction: 2NO(g) + 5H₂(g) → 2NH₃(g) + 2H₂O(l) 30.01g/mol 2.016g/mol 17.034g/mol 18.016g/mol If 86.3g NO and 25.6g H₂ are mixed and allowed to react as much as possible, what is the theoretical yield of ammonia in grams? Limiting reactant (LR) % yield = actual yield / theoretical yield × 100% 86.3g NO × (1mol NO / 30.01g NO) × (2mol NH₃ / 2mol NO) = 2.8757 moles NH₃ 25.6g H₂ × (1mol H₂ / 2.016g H₂) × (2mol NH₃ / 5mol H₂) = 5.0794 moles NH₃ Calc Ty: 2.8757mol NH₃ × (17.034g NH₃ / 1mol NH₃) = 49.0g NH₃