Atom Economy | A-level Chemistry | OCR, AQA, Edexcel

Introduction

This tutorial will provide you with a comprehensive understanding of atom economy, a key concept in A-level Chemistry. You'll learn what atom economy is, how to calculate it, its significance in reducing waste, and the different types of reactions based on their atom economy.

Step 1: Understand Atom Economy

Atom economy is defined as the mass of the desired product as a percentage of the mass of all products formed in a chemical reaction. It can be calculated using the following formula:

Atom Economy = (Mass of Desired Product / Mass of All Products) x 100%

Practical Advice

• Focus on identifying both the desired product and the total mass of all products when analyzing a reaction.
• A higher atom economy indicates a more efficient reaction with less waste.

Step 2: Calculate Atom Economy with a Worked Example

Let’s calculate the atom economy for the production of dichloromethane (CH2Cl2) from the following reaction:

2Cl2 + CH4 → CH2Cl2 + 2HCl

Steps to Calculate

1. Identify the desired product: CH2Cl2
2. Calculate the mass of the desired product:
   • Molar mass of CH2Cl2 = 12.01 (C) + 21.01 (H) + 235.45 (Cl) = 84.93 g/mol
3. Calculate the total mass of all products:
   • CH2Cl2 (84.93 g/mol) + 2HCl (2 * 36.46 g/mol) = 84.93 + 72.92 = 157.85 g/mol
4. Apply the formula:

   Atom Economy = (84.93 / 157.85) x 100% ≈ 53.8%
   

Practical Advice

• Always verify the molar masses of the compounds involved to ensure accurate calculations.
• Practice with different reactions to become comfortable with the concept.

Step 3: Recognize the Importance of Atom Economy

Understanding atom economy is crucial for several reasons:

• It helps to minimize chemical waste, leading to more sustainable practices.
• Higher atom economy reflects greater efficiency in chemical processes.
• It allows chemists to assess the feasibility of reactions in industrial applications.

Common Pitfalls

• Neglecting to account for unwanted by-products can lead to inaccurate calculations.
• Overlooking the significance of atom economy in relation to environmental impact.

Step 4: Identify Types of Reactions

Different types of reactions exhibit varying atom economies:

Addition Reactions

• Achieve 100% atom economy.
• No by-products are formed.
• Example: The reaction of alkenes with hydrogen.

Substitution and Elimination Reactions

• Have less than 100% atom economy.
• Typically generate by-products.
• Example: Halogenation reactions.

Practical Advice

• Familiarize yourself with examples of each reaction type to better understand their atom economies.
• Analyze reactions in your coursework to predict their atom economy based on the type of reaction.

Conclusion

In this tutorial, you learned about atom economy, how to calculate it, its importance in reducing chemical waste, and the different types of reactions based on their efficiencies. By applying this knowledge, you can enhance your understanding of chemical processes and contribute to more sustainable practices in chemistry. Next, consider exploring real-world applications of atom economy in industrial chemistry or reviewing additional examples to solidify your understanding.