Year 10 Chemistry: Yield and Atom Economy of Chemical Reactions

Introduction to Yield

What is Yield?

In chemistry, yield refers to the amount of product that is produced in a chemical reaction. It tells us how efficient a reaction is.

Types of Yield

1. Theoretical Yield: This is the maximum amount of product that could be formed from the reactants, according to the balanced chemical equation.
2. Actual Yield: This is the amount of product that you actually obtain from the reaction when you perform it in the lab.

Yield Calculation

To find the percentage yield, you can use this formula:

$$\text{Percentage Yield} = \left( \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \right) \times 100$$

Example of Yield

Let’s say you perform a reaction and you expect to get 10 grams of product (theoretical yield), but you only collect 8 grams (actual yield). The calculation would look like this:

$$\text{Percentage Yield} = \left( \frac{8 \text{ g}}{10 \text{ g}} \right) \times 100 = 80%$$

Introduction to Atom Economy

What is Atom Economy?

Atom economy measures how well atoms are utilized in a chemical reaction. It tells us how many of the reactant atoms are converted into useful products.

Importance of Atom Economy

High atom economy means more of the reactants are turned into useful products, which is better for the environment and more economical.

Atom Economy Calculation

To calculate atom economy, you can use this formula:

$$\text{Atom Economy} = \left( \frac{\text{Molar Mass of Desired Product}}{\text{Total Molar Mass of Reactants}} \right) \times 100$$

Example of Atom Economy

Imagine a reaction where two reactants combine to form one product. If the molar mass of the product is 18 g/mol and the total molar mass of the reactants is 36 g/mol, the atom economy would be:

$$\text{Atom Economy} = \left( \frac{18 \text{ g/mol}}{36 \text{ g/mol}} \right) \times 100 = 50%$$

Key Rules, Tips, and Tricks

• Always balance your chemical equations before calculating yield or atom economy. This ensures accurate results.
• To improve yield, consider factors like temperature, pressure, and concentration of reactants.
• For higher atom economy, look for reactions that produce fewer by-products.
• Keep in mind that both yield and atom economy are important for evaluating the efficiency of reactions.

Questions

Easy Level Questions

1. What does yield measure in a chemical reaction?
2. What is the formula for calculating percentage yield?
3. If the theoretical yield is 12 grams and the actual yield is 9 grams, what is the percentage yield?
4. Define actual yield in your own words.
5. What is atom economy?
6. Why is atom economy important?
7. What is the formula for calculating atom economy?
8. If the molar mass of the product is 20 g/mol and the total molar mass of the reactants is 40 g/mol, what is the atom economy?
9. What do we call the maximum amount of product that can be formed in a reaction?
10. What does a high atom economy indicate?

Medium Level Questions

11. Calculate the percentage yield if the actual yield is 5 grams and the theoretical yield is 10 grams.
12. Explain why actual yield is often less than theoretical yield.
13. If a reaction has an atom economy of 75%, what does that mean for the reactants?
14. Why might a chemist want to increase the atom economy of a reaction?
15. If a product has a molar mass of 30 g/mol and the total molar mass of reactants is 90 g/mol, what is the atom economy?
16. Describe one way to improve the yield of a chemical reaction.
17. If the actual yield of a reaction is 3 grams and the theoretical yield is 9 grams, calculate the percentage yield.
18. What is a by-product in a chemical reaction?
19. Why is it important to consider both yield and atom economy in green chemistry?
20. If a reaction produces 5 grams of by-products, how does that affect the atom economy?

Hard Level Questions

21. A reaction produces 50 grams of desired product with a theoretical yield of 60 grams. Calculate the percentage yield.
22. A chemist performs a reaction with a total molar mass of reactants equal to 100 g/mol. If the desired product has a molar mass of 25 g/mol, what is the atom economy?
23. Explain how temperature can affect the yield of a reaction.
24. If a reaction has a low atom economy, what might this suggest about the efficiency of the reaction?
25. Discuss how the percentage yield and atom economy can impact the cost of producing a chemical product.
26. If the theoretical yield is 80 grams and the actual yield is 64 grams, what is the percentage yield?
27. A reaction is said to have an atom economy of 90%. What does this imply about waste products?
28. If a reaction produces multiple products, how can you determine which one to consider for atom economy?
29. Explain how catalyst use can lead to higher yields in reactions.
30. Compare and contrast percentage yield and atom economy.

Answers

Easy Level Answers

1. Yield measures the amount of product produced.
2. $$\text{Percentage Yield} = \left( \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \right) \times 100$$
3. $$\text{Percentage Yield} = \left( \frac{9}{12} \right) \times 100 = 75%$$
4. Actual yield is the amount of product you get from a reaction.
5. Atom economy measures how well atoms are used in a reaction.
6. It’s important because it shows how efficiently reactants are converted to products.
7. $$\text{Atom Economy} = \left( \frac{\text{Molar Mass of Desired Product}}{\text{Total Molar Mass of Reactants}} \right) \times 100$$
8. $$\text{Atom Economy} = \left( \frac{20}{40} \right) \times 100 = 50%$$
9. The maximum amount of product is called theoretical yield.
10. A high atom economy means less waste and better efficiency.

Medium Level Answers

11. $$\text{Percentage Yield} = \left( \frac{5}{10} \right) \times 100 = 50%$$
12. Actual yield is less because of side reactions, incomplete reactions, or losses during collection.
13. It means that some reactant atoms were not converted to the desired product.
14. To reduce waste and improve cost-effectiveness.
15. $$\text{Atom Economy} = \left( \frac{30}{90} \right) \times 100 = 33.33%$$
16. Increasing the concentration of reactants can improve yield.
17. $$\text{Percentage Yield} = \left( \frac{3}{9} \right) \times 100 = 33.33%$$
18. A by-product is an unwanted product formed during a reaction.
19. They help evaluate the sustainability and economic feasibility of a process.
20. It can lower the atom economy since fewer reactants are converted to the desired product.

Hard Level Answers

21. $$\text{Percentage Yield} = \left( \frac{50}{60} \right) \times 100 = 83.33%$$
22. $$\text{Atom Economy} = \left( \frac{25}{100} \right) \times 100 = 25%$$
23. Higher temperatures can increase reaction rates, but may also lead to side reactions.
24. It suggests that a lot of reactant atoms are wasted as by-products.
25. Higher costs can arise from low yields and high waste, making products less economical.
26. $$\text{Percentage Yield} = \left( \frac{64}{80} \right) \times 100 = 80%$$
27. It implies that the reaction produces very little waste compared to reactants.
28. The product with the highest value or lowest waste should be considered.
29. Catalysts can speed up reactions without being consumed, leading to higher yields.
30. Percentage yield focuses on recovery of product, while atom economy focuses on waste minimization.

Feel free to ask any questions if you need clarification on any of the topics!