Percentage Yield
\( \% \text{Yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100 \)
The theoretical yield is the maximum amount of product calculated from stoichiometry (using the limiting reagent). The actual yield is what you actually obtain experimentally — always less because of:
- Incomplete reactions (equilibrium stops short)
- Side reactions producing unwanted products
- Losses during transfer, filtration, or purification
Atom Economy
\( \% \text{AE} = \frac{M_r \text{ of desired product}}{M_r \text{ of all products}} \times 100 \)
Atom economy measures how much of the reactant atoms end up in the useful product. High atom economy = less waste = more sustainable.
Addition Reaction
C₂H₄ + HBr → C₂H₅Br
All atoms end up in the product
Substitution Reaction
C₂H₆ + Br₂ → C₂H₅Br + HBr
HBr is a by-product (waste)
Think About It
A reaction has 100% atom economy but only 30% yield. Is it efficient?
Not necessarily. Atom economy measures the potential efficiency of the reaction pathway, while yield measures actual success. A reaction needs both high AE and high yield to be truly efficient and sustainable.