University:
Mississippi College
Course:
CHE 141 | General Chemistry I
Academic year:

2022
Views:

361

Pages:

2
Author:

Abby D.

CH.4 Limiting Reactant, Theoretical Yield & Percent Yield Limiting Reactant -> AKA limiting reagent (mixing in the lab) 4 definitions! ① The limiting Reactant is the reactant that runs out first (consumed) ② When it is consumed (runs out), the reactant stops ③ The reaction that "limits" the amount of product formed (yield) ④ The LR is the one that has the potential to make the least amount of product. [Diagram: 10 bread slices + Peanut butter (jar) + Jelly (jar) + Spoon (cat) -> PB&J Sandwiches] (less) runs out faster (LR) consider this reaction: N₂ + 3H₂ → 2NH₃ ? 10.0 mol N₂ is reacted w/ 15.0 mol H₂. Which one is the LR? (which one can make the least amt of product?) (Run two "tests") @ LR? Ⓑ TY 10.0 mol N₂ x (2 mol NH₃ / 1 mol N₂) = 20.0 mol NH₃ "in excess" 15.0 mol H₂ x (2 mol NH₃ / 3 mol H₂) = 10.0 mol NH₃ ↑ LR Theoretical yield (17.034g / 1mol) = 170.34g -> 170g 1.70 x 10²g ↳ use this for PY Ⓒ If 15.5g NH₃ were produced calc. % yield? PY = (15.5g / 170.34g) x 100 = 90.99% -> 91.0% Theoretical yield - The amt of product made by the LR! (moles or grams) Percent Yield - (AY / TY) x 100 (actual yield) Consider this rxn: P₄ + 6Cl₂ → 4PCl₃ ? 45.2g P₄ reacts w/ 351.8g Cl₂. 85.2g PCl₃ is produced. Identify the LR, calc the TY of PCl₃ + calc the % yield. AY (produced) LR ↑ 45.2g P₄ x (1mol P₄ / 123.88g P₄) x (4mol PCl₃ / 1mol P₄) x (137.32g / 1mol PCl₃) = 200.42g PCl₃ -> 200g 2.00 x 10²g PCl₃ TY ↑ 351.8g Cl₂ x (1mol Cl₂ / 70.9g) x (4mol PCl₃ / 6mol Cl₂) x (137.32g / 1mol) = 454.25g PCl₃ PY = (85.2g / 200.42) x 100 = 42.5% Fe₂O₃ + 3CO → 2Fe + 3CO₂ ? 13.5mg of Iron (III) oxide reacts w/ 1.50g Carbon monoxide. 8.3mg CO₂ is collected. a) identify the LR. b) calc the % yield. AY ↑ LR ↑ 13.5mg Fe₂O₃ x (1g / 1000mg) x (1mol Fe₂O₃ / 159.7g) x (3mol CO₂ / 1mol Fe₂O₃) x (44.01g / 1mol) = 0.01116g CO₂ TY ↑ 0.0112g CO₂ 1.50g CO x (1mol CO / 28.01g) x (3mol CO₂ / 3mol CO) x (44.01g / 1mol) = 2.3568g CO₂ "in excess" PY = (8.3mg / 0.0112g) x 100 (0.0083g / 0.0112g) x 100 = 74.11 -> 74% bcs SF=2 8.3mg x (1g / 1000mg) = 0.0083g