31. Atom Economy: Calculations & Importance

Atom Economy: Calculations & Importance

Based on the video, here are the notes on atom economy, how to calculate it, and why it is a vital consideration in industrial chemistry.

1. What is Atom Economy?

  • Definition: Atom economy is a measure of the amount of starting materials (reactants) that end up as useful products.

  • Useful vs. Waste: In many industrial reactions, multiple products are formed. Usually, only one or two are "desired," while the others are considered "waste."

  • Ideal Scenario: A reaction where the desired product is the only product has an atom economy of 100% (e.g., Nitrogen + Hydrogen → Ammonia).

2. The Atom Economy Formula

To find the atom economy as a percentage, use the following calculation:

Atom Economy = (Mr of Desired Product / Total Mr of All Reactants) × 100

  • Example Calculation: Reacting carbon monoxide (Mr = 28) and water (Mr = 18) to make hydrogen (desired product, Mr = 2) and carbon dioxide.

    • Step 1: Find total Mr of reactants: 28 + 18 = 46.

    • Step 2: Divide Mr of desired product by total reactant Mr: 2 / 46 = 0.0435.

    • Step 3: Multiply by 100: 4.35%.

  • Note: This is a very low atom economy, meaning over 95% of the reactants become waste.

3. Why Atom Economy is Important

Industrial companies aim for high atom economy for three main reasons:

  1. Cost of Raw Materials: Raw materials are expensive. If most of them turn into waste, the process is less profitable.

  2. Sustainability: It is unsustainable to use large amounts of reactants to produce tiny amounts of useful products.

  3. Waste Disposal: Waste products can be expensive to dispose of safely and can damage the environment.

4. Improving Profitability

  • Finding a Use for Waste: The best way to improve a process is to find a use for the "waste" products. If they can be used or sold, they become "useful by-products," effectively increasing the economy of the process.

  • Alternative Reactions: Companies may look for a different chemical reaction that produces the same desired product but with fewer or more useful side products.

5. Other Factors in Industrial Chemistry

While atom economy is important, companies also consider:

  • Percentage Yield: How much product is actually made compared to the maximum possible.

  • Rate of Reaction: How fast the product is made.

  • Equilibrium Position: Especially for reversible reactions.

  • Cost of Conditions: The energy required to maintain high temperatures or pressures.