% Yield

Introduction

• The class is different yet similar, an engaging aspect of the course.
• Technical difficulties with the microphone.

Class Overview

• Discussion on preparation for the second exam and notices related to class schedules.
  • Academic shutdown on Monday and Tuesday for study days.
  • No discussion sections or office hours on those days.
  • Regular classes resume on Wednesday.

Percent Yield and Reaction Yields

• Focus on percent yield and stoichiometry in chemical reactions.
• Definitions:
  • Percent Yield: A value used to judge how well a reaction performed, ideally should be maximized.
• Importance: Higher percent yield indicates better reaction conditions.

Stoichiometry Basics

• To get successful reactions, it's often necessary to adjust the quantities of reactants:
  • Adherence to the stoichiometric ratios is crucial but may need adjustments based on experimental outcomes.
• Factors affecting yield include:
  • Mixing ratios.
  • Reaction conditions such as stirring method, temperature, and reaction time.

Determining Theoretical and Actual Yield

• Actual Yield: The amount produced in the lab after purification processes, deviations can occur.
• Theoretical Yield: Maximum possible amount of product based on stoichiometry and limiting reagents.
• Limiting Reagent: The reactant that is completely consumed first during the reaction, determines the theoretical yield.

Example: Cooking with Reagents (Pizza)

• Ingredients for Pizza:
  • 4 pizza crusts, 10 cups of cheese, 15 ounces of tomato sauce.
  • Requirements: Per pizza - 5 ounces of tomato sauce, 2 cups of cheese.
• Yield Calculation:
  • Cheese allows for 5 pizzas; Sauce limits to 3 pizzas (limiting reagent).
  • Theoretical Yield: 3 pizzas.
  • Actual Yield: 2 pizzas dropped.
• Percent Yield Calculation:
  • Percent Yield = (Actual Yield / Theoretical Yield) x 100 = (2 / 3) x 100 = 66.67%.

Real-World Example: Popping Popcorn

• Typically, not all kernels pop.
• Starting with 20 kernels, finding 16 popped means:
  • Theoretical Yield: 20.
  • Actual Yield: 16.
  • Percent Yield Calculation: (16 / 20) x 100 = 80%.

Stoichiometry in Chemical Reactions

• Students will encounter problems where:
  • Amounts and excess reagents are provided or need to be calculated.
• Example Reaction: P4 + Cl2 for forming PCl_3.
  • Calculating Moles: Given amounts need conversion to identify limiting reagent.
• Implications of Excess: Generally, gas is used as excess because it is easily discarded after reactions.

Thermite Reaction for Welding

- A practical application of chemistry in the field.

The Reaction: Iron Oxide + Aluminum

• Reaction conditions produce molten iron for