Yield & Economy
How much product does a reaction really make, and how much of the atoms are wasted? Learn percentage yield, atom economy, why yield is rarely 100%, and why atom economy matters for a greener chemistry.
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Making the most of a reaction ⚗️
Chemists care about two questions: **how much** product did we actually get, and how much of the reactants was **wasted**? The first is measured by **percentage yield**, the second by **atom economy**. Both matter for cost and for the environment - and both come down to a simple calculation.
The words you need 🔑
Four ideas run through the topic:
Match each term to its meaning 🔗
- Actual yield
- Theoretical yield
- Percentage yield
- Atom economy
- The mass of product you really got
- The maximum mass the reaction could make
- Actual divided by theoretical, times 100
- How much of the atoms become useful product
The yield formula 🧮
How do you calculate the percentage yield of a reaction?
- Actual mass divided by theoretical mass, times 100
- Theoretical mass divided by actual mass, times 100
- Actual mass added to theoretical mass
- Actual mass multiplied by theoretical mass
Two useful measures 📋
Learn both calculations: - **Percentage yield = (actual mass / theoretical mass) x 100** - **Atom economy = (Mr of the desired product / total Mr of all products) x 100** Yield is rarely 100%: reactions can be incomplete or reversible, side reactions occur, and product is lost when it is transferred and purified.
Why is yield below 100%? ✅
Select the TWO genuine reasons a reaction gives less than a 100% yield.
- Some product is lost when it is transferred or purified
- The reaction may be reversible or incomplete
- Atoms are destroyed during the reaction
- The balance always reads too high
Yield versus atom economy ⚖️
Two different questions about the same reaction.
Percentage yield 💯
An interactive activity.
Why atom economy matters ♻️
Why do industries prefer reactions with a high atom economy?
- Less is wasted, so it is cheaper and more sustainable
- It always makes the reaction happen faster
- It makes the reaction give out more heat
- It makes the product a brighter colour
Atom economy ➗
An interactive activity.
Put it together 🧱
Percentage _____ compares the actual mass of product with the _____ maximum. It is often below 100% because of _____ and side reactions. _____ economy measures how much of the atoms become useful product, and a high value means less _____.
Work out a yield 🪜
An interactive activity.
Choose the greener route 🧭
An interactive activity.
The grade-9 habit 🌟
Keep the **two measures separate**. Percentage yield is about the **amount** you actually got (lowered by losses and side reactions). Atom economy is about how many of the **atoms** are useful (fixed by the equation). For top marks, **link them to sustainability**: a high atom economy wastes fewer reactants, cutting cost and environmental impact. Right formula, right reasoning, clear link to green chemistry - top band.